diff --git a/Makefile.am b/Makefile.am
index 6223301..7db38f0 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -82,6 +82,8 @@
   csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj                \
   csharp/src/Google.Protobuf.Test/IssuesTest.cs                              \
   csharp/src/Google.Protobuf.Test/JsonFormatterTest.cs                       \
+  csharp/src/Google.Protobuf.Test/JsonParserTest.cs                          \
+  csharp/src/Google.Protobuf.Test/JsonTokenizerTest.cs                       \
   csharp/src/Google.Protobuf.Test/Properties/AppManifest.xml                 \
   csharp/src/Google.Protobuf.Test/Properties/AssemblyInfo.cs                 \
   csharp/src/Google.Protobuf.Test/Reflection/DescriptorsTest.cs              \
@@ -119,6 +121,9 @@
   csharp/src/Google.Protobuf/IMessage.cs                                     \
   csharp/src/Google.Protobuf/InvalidProtocolBufferException.cs               \
   csharp/src/Google.Protobuf/JsonFormatter.cs                                \
+  csharp/src/Google.Protobuf/JsonParser.cs                                   \
+  csharp/src/Google.Protobuf/JsonToken.cs                                    \
+  csharp/src/Google.Protobuf/JsonTokenizer.cs                                \
   csharp/src/Google.Protobuf/LimitedInputStream.cs                           \
   csharp/src/Google.Protobuf/MessageExtensions.cs                            \
   csharp/src/Google.Protobuf/MessageParser.cs                                \
diff --git a/csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj b/csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
index 33be5da..cd15b96 100644
--- a/csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
+++ b/csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
@@ -95,6 +95,8 @@
     <Compile Include="Collections\MapFieldTest.cs" />
     <Compile Include="Collections\RepeatedFieldTest.cs" />
     <Compile Include="JsonFormatterTest.cs" />
+    <Compile Include="JsonParserTest.cs" />
+    <Compile Include="JsonTokenizerTest.cs" />
     <Compile Include="Reflection\DescriptorsTest.cs" />
     <Compile Include="Reflection\FieldAccessTest.cs" />
     <Compile Include="SampleEnum.cs" />
diff --git a/csharp/src/Google.Protobuf.Test/JsonFormatterTest.cs b/csharp/src/Google.Protobuf.Test/JsonFormatterTest.cs
index 3e7a3d2..08cedad 100644
--- a/csharp/src/Google.Protobuf.Test/JsonFormatterTest.cs
+++ b/csharp/src/Google.Protobuf.Test/JsonFormatterTest.cs
@@ -276,6 +276,13 @@
         }
 
         [Test]
+        public void WrapperFormatting_Message()
+        {
+            Assert.AreEqual("\"\"", JsonFormatter.Default.Format(new StringValue()));
+            Assert.AreEqual("0", JsonFormatter.Default.Format(new Int32Value()));
+        }
+
+        [Test]
         public void WrapperFormatting_IncludeNull()
         {
             // The actual JSON here is very large because there are lots of fields. Just test a couple of them.
@@ -376,12 +383,12 @@
             {
                 Fields =
                 {
-                    { "a", new Value { NullValue = new NullValue() } },
-                    { "b", new Value { BoolValue = false } },
-                    { "c", new Value { NumberValue = 10.5 } },
-                    { "d", new Value { StringValue = "text" } },
-                    { "e", new Value { ListValue = new ListValue { Values = { new Value { StringValue = "t1" }, new Value { NumberValue = 5 } } } } },
-                    { "f", new Value { StructValue = new Struct { Fields = { { "nested", new Value { StringValue = "value" } } } } } }
+                    { "a", Value.ForNull() },
+                    { "b", Value.ForBool(false) },
+                    { "c", Value.ForNumber(10.5) },
+                    { "d", Value.ForString("text") },
+                    { "e", Value.ForList(Value.ForString("t1"), Value.ForNumber(5)) },
+                    { "f", Value.ForStruct(new Struct { Fields = { { "nested", Value.ForString("value") } } }) }
                 }
             };
             AssertJson("{ 'a': null, 'b': false, 'c': 10.5, 'd': 'text', 'e': [ 't1', 5 ], 'f': { 'nested': 'value' } }", message.ToString());
@@ -405,6 +412,14 @@
             AssertJson("{ 'fieldMaskField': 'user.displayName,photo' }", JsonFormatter.Default.Format(message));
         }
 
+        // SourceContext is an example of a well-known type with no special JSON handling
+        [Test]
+        public void SourceContextStandalone()
+        {
+            var message = new SourceContext { FileName = "foo.proto" };
+            AssertJson("{ 'fileName': 'foo.proto' }", JsonFormatter.Default.Format(message));
+        }
+
         /// <summary>
         /// Checks that the actual JSON is the same as the expected JSON - but after replacing
         /// all apostrophes in the expected JSON with double quotes. This basically makes the tests easier
diff --git a/csharp/src/Google.Protobuf.Test/JsonParserTest.cs b/csharp/src/Google.Protobuf.Test/JsonParserTest.cs
new file mode 100644
index 0000000..b1c7b46
--- /dev/null
+++ b/csharp/src/Google.Protobuf.Test/JsonParserTest.cs
@@ -0,0 +1,727 @@
+﻿#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+using Google.Protobuf.TestProtos;
+using Google.Protobuf.WellKnownTypes;
+using NUnit.Framework;
+using System;
+
+namespace Google.Protobuf
+{
+    /// <summary>
+    /// Unit tests for JSON parsing. Some tests are ignored at the moment as the desired behaviour
+    /// isn't fully known, either in terms of which exceptions should be thrown or whether they should
+    /// count as valid values.
+    /// </summary>
+    public class JsonParserTest
+    {
+        // Sanity smoke test
+        [Test]
+        public void AllTypesRoundtrip()
+        {
+            AssertRoundtrip(SampleMessages.CreateFullTestAllTypes());
+        }
+
+        [Test]
+        public void Maps()
+        {
+            AssertRoundtrip(new TestMap { MapStringString = { { "with spaces", "bar" }, { "a", "b" } } });
+            AssertRoundtrip(new TestMap { MapInt32Int32 = { { 0, 1 }, { 2, 3 } } });
+            AssertRoundtrip(new TestMap { MapBoolBool = { { false, true }, { true, false } } });
+        }
+
+        [Test]
+        [TestCase(" 1 ")]
+        [TestCase("+1")]
+        [TestCase("1,000")]
+        [TestCase("1.5")]
+        public void IntegerMapKeysAreStrict(string keyText)
+        {
+            // Test that integer parsing is strict. We assume that if this is correct for int32,
+            // it's correct for other numeric key types.
+            var json = "{ \"mapInt32Int32\": { \"" + keyText + "\" : \"1\" } }";
+            Assert.Throws<InvalidProtocolBufferException>(() => JsonParser.Default.Parse<TestMap>(json));
+        }
+
+        [Test]
+        public void SourceContextRoundtrip()
+        {
+            AssertRoundtrip(new SourceContext { FileName = "foo.proto" });
+        }
+
+        [Test]
+        public void SingularWrappers_DefaultNonNullValues()
+        {
+            var message = new TestWellKnownTypes
+            {
+                StringField = "",
+                BytesField = ByteString.Empty,
+                BoolField = false,
+                FloatField = 0f,
+                DoubleField = 0d,
+                Int32Field = 0,
+                Int64Field = 0,
+                Uint32Field = 0,
+                Uint64Field = 0
+            };
+            AssertRoundtrip(message);
+        }
+
+        [Test]
+        public void SingularWrappers_NonDefaultValues()
+        {
+            var message = new TestWellKnownTypes
+            {
+                StringField = "x",
+                BytesField = ByteString.CopyFrom(1, 2, 3),
+                BoolField = true,
+                FloatField = 12.5f,
+                DoubleField = 12.25d,
+                Int32Field = 1,
+                Int64Field = 2,
+                Uint32Field = 3,
+                Uint64Field = 4
+            };
+            AssertRoundtrip(message);
+        }
+
+        [Test]
+        public void SingularWrappers_ExplicitNulls()
+        {
+            var message = new TestWellKnownTypes();
+            var json = new JsonFormatter(new JsonFormatter.Settings(true)).Format(message);
+            var parsed = JsonParser.Default.Parse<TestWellKnownTypes>(json);
+            Assert.AreEqual(message, parsed);
+        }
+
+        [Test]
+        [TestCase(typeof(Int32Value), "32", 32)]
+        [TestCase(typeof(Int64Value), "32", 32L)]
+        [TestCase(typeof(UInt32Value), "32", 32U)]
+        [TestCase(typeof(UInt64Value), "32", 32UL)]
+        [TestCase(typeof(StringValue), "\"foo\"", "foo")]
+        [TestCase(typeof(FloatValue), "1.5", 1.5f)]
+        [TestCase(typeof(DoubleValue), "1.5", 1.5d)]
+        public void Wrappers_Standalone(System.Type wrapperType, string json, object expectedValue)
+        {
+            IMessage parsed = (IMessage) Activator.CreateInstance(wrapperType);
+            IMessage expected = (IMessage) Activator.CreateInstance(wrapperType);
+            JsonParser.Default.Merge(parsed, "null");
+            Assert.AreEqual(expected, parsed);
+
+            JsonParser.Default.Merge(parsed, json);
+            expected.Descriptor.Fields[Wrappers.WrapperValueFieldNumber].Accessor.SetValue(expected, expectedValue);
+            Assert.AreEqual(expected, parsed);
+        }
+
+        [Test]
+        public void BytesWrapper_Standalone()
+        {
+            ByteString data = ByteString.CopyFrom(1, 2, 3);
+            // Can't do this with attributes...
+            var parsed = JsonParser.Default.Parse<BytesValue>("\"" + data.ToBase64() + "\"");
+            var expected = new BytesValue { Value = data };
+            Assert.AreEqual(expected, parsed);
+        }
+
+        [Test]
+        public void RepeatedWrappers()
+        {
+            var message = new RepeatedWellKnownTypes
+            {
+                BoolField = { true, false },
+                BytesField = { ByteString.CopyFrom(1, 2, 3), ByteString.CopyFrom(4, 5, 6), ByteString.Empty },
+                DoubleField = { 12.5, -1.5, 0d },
+                FloatField = { 123.25f, -20f, 0f },
+                Int32Field = { int.MaxValue, int.MinValue, 0 },
+                Int64Field = { long.MaxValue, long.MinValue, 0L },
+                StringField = { "First", "Second", "" },
+                Uint32Field = { uint.MaxValue, uint.MinValue, 0U },
+                Uint64Field = { ulong.MaxValue, ulong.MinValue, 0UL },
+            };
+            AssertRoundtrip(message);
+        }
+
+        [Test]
+        public void IndividualWrapperTypes()
+        {
+            Assert.AreEqual(new StringValue { Value = "foo" }, StringValue.Parser.ParseJson("\"foo\""));
+            Assert.AreEqual(new Int32Value { Value = 1 }, Int32Value.Parser.ParseJson("1"));
+            // Can parse strings directly too
+            Assert.AreEqual(new Int32Value { Value = 1 }, Int32Value.Parser.ParseJson("\"1\""));
+        }
+
+        private static void AssertRoundtrip<T>(T message) where T : IMessage<T>, new()
+        {
+            var clone = message.Clone();
+            var json = message.ToString();
+            var parsed = JsonParser.Default.Parse<T>(json);
+            Assert.AreEqual(clone, parsed);
+        }
+
+        [Test]
+        [TestCase("0", 0)]
+        [TestCase("-0", 0)] // Not entirely clear whether we intend to allow this...
+        [TestCase("1", 1)]
+        [TestCase("-1", -1)]
+        [TestCase("2147483647", 2147483647)]
+        [TestCase("-2147483648", -2147483648)]
+        public void StringToInt32_Valid(string jsonValue, int expectedParsedValue)
+        {
+            string json = "{ \"singleInt32\": \"" + jsonValue + "\"}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleInt32);
+        }
+
+        [Test]
+        [TestCase("+0")]
+        [TestCase("00")]
+        [TestCase("-00")]
+        [TestCase("--1")]
+        [TestCase("+1")]
+        [TestCase("1.5")]
+        [TestCase("1e10")]
+        [TestCase("2147483648")]
+        [TestCase("-2147483649")]
+        public void StringToInt32_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleInt32\": \"" + jsonValue + "\"}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0U)]
+        [TestCase("1", 1U)]
+        [TestCase("4294967295", 4294967295U)]
+        public void StringToUInt32_Valid(string jsonValue, uint expectedParsedValue)
+        {
+            string json = "{ \"singleUint32\": \"" + jsonValue + "\"}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleUint32);
+        }
+
+        // Assume that anything non-bounds-related is covered in the Int32 case
+        [Test]
+        [TestCase("-1")]
+        [TestCase("4294967296")]
+        public void StringToUInt32_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleUint32\": \"" + jsonValue + "\"}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0L)]
+        [TestCase("1", 1L)]
+        [TestCase("-1", -1L)]
+        [TestCase("9223372036854775807", 9223372036854775807)]
+        [TestCase("-9223372036854775808", -9223372036854775808)]
+        public void StringToInt64_Valid(string jsonValue, long expectedParsedValue)
+        {
+            string json = "{ \"singleInt64\": \"" + jsonValue + "\"}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleInt64);
+        }
+
+        // Assume that anything non-bounds-related is covered in the Int32 case
+        [Test]
+        [TestCase("-9223372036854775809")]
+        [TestCase("9223372036854775808")]
+        public void StringToInt64_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleInt64\": \"" + jsonValue + "\"}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0UL)]
+        [TestCase("1", 1UL)]
+        [TestCase("18446744073709551615", 18446744073709551615)]
+        public void StringToUInt64_Valid(string jsonValue, ulong expectedParsedValue)
+        {
+            string json = "{ \"singleUint64\": \"" + jsonValue + "\"}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleUint64);
+        }
+
+        // Assume that anything non-bounds-related is covered in the Int32 case
+        [Test]
+        [TestCase("-1")]
+        [TestCase("18446744073709551616")]
+        public void StringToUInt64_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleUint64\": \"" + jsonValue + "\"}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0d)]
+        [TestCase("1", 1d)]
+        [TestCase("1.000000", 1d)]
+        [TestCase("1.0000000000000000000000001", 1d)] // We don't notice that we haven't preserved the exact value
+        [TestCase("-1", -1d)]
+        [TestCase("1e1", 10d)]
+        [TestCase("1e01", 10d)] // Leading decimals are allowed in exponents
+        [TestCase("1E1", 10d)] // Either case is fine
+        [TestCase("-1e1", -10d)]
+        [TestCase("1.5e1", 15d)]
+        [TestCase("-1.5e1", -15d)]
+        [TestCase("15e-1", 1.5d)]
+        [TestCase("-15e-1", -1.5d)]
+        [TestCase("1.79769e308", 1.79769e308)]
+        [TestCase("-1.79769e308", -1.79769e308)]
+        [TestCase("Infinity", double.PositiveInfinity)]
+        [TestCase("-Infinity", double.NegativeInfinity)]
+        [TestCase("NaN", double.NaN)]
+        public void StringToDouble_Valid(string jsonValue, double expectedParsedValue)
+        {
+            string json = "{ \"singleDouble\": \"" + jsonValue + "\"}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleDouble);
+        }
+
+        [Test]
+        [TestCase("1.7977e308")]
+        [TestCase("-1.7977e308")]
+        [TestCase("1e309")]
+        [TestCase("1,0")]
+        [TestCase("1.0.0")]
+        [TestCase("+1")]
+        [TestCase("00")]
+        [TestCase("--1")]
+        [TestCase("\u00BD")] // 1/2 as a single Unicode character. Just sanity checking...
+        public void StringToDouble_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleDouble\": \"" + jsonValue + "\"}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0f)]
+        [TestCase("1", 1f)]
+        [TestCase("1.000000", 1f)]
+        [TestCase("-1", -1f)]
+        [TestCase("3.402823e38", 3.402823e38f)]
+        [TestCase("-3.402823e38", -3.402823e38f)]
+        [TestCase("1.5e1", 15f)]
+        [TestCase("15e-1", 1.5f)]
+        public void StringToFloat_Valid(string jsonValue, float expectedParsedValue)
+        {
+            string json = "{ \"singleFloat\": \"" + jsonValue + "\"}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleFloat);
+        }
+
+        [Test]
+        [TestCase("3.402824e38")]
+        [TestCase("-3.402824e38")]
+        [TestCase("1,0")]
+        [TestCase("1.0.0")]
+        [TestCase("+1")]
+        [TestCase("00")]
+        [TestCase("--1")]
+        public void StringToFloat_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleFloat\": \"" + jsonValue + "\"}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0)]
+        [TestCase("-0", 0)] // Not entirely clear whether we intend to allow this...
+        [TestCase("1", 1)]
+        [TestCase("-1", -1)]
+        [TestCase("2147483647", 2147483647)]
+        [TestCase("-2147483648", -2147483648)]
+        public void NumberToInt32_Valid(string jsonValue, int expectedParsedValue)
+        {
+            string json = "{ \"singleInt32\": " + jsonValue + "}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleInt32);
+        }
+
+        [Test]
+        [TestCase("+0")]
+        [TestCase("00")]
+        [TestCase("-00")]
+        [TestCase("--1")]
+        [TestCase("+1")]
+        [TestCase("1.5", Ignore = true, Reason = "Desired behaviour unclear")]
+        [TestCase("1e10")]
+        [TestCase("2147483648")]
+        [TestCase("-2147483649")]
+        public void NumberToInt32_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleInt32\": " + jsonValue + "}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0U)]
+        [TestCase("1", 1U)]
+        [TestCase("4294967295", 4294967295U)]
+        public void NumberToUInt32_Valid(string jsonValue, uint expectedParsedValue)
+        {
+            string json = "{ \"singleUint32\": " + jsonValue + "}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleUint32);
+        }
+
+        // Assume that anything non-bounds-related is covered in the Int32 case
+        [Test]
+        [TestCase("-1")]
+        [TestCase("4294967296")]
+        public void NumberToUInt32_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleUint32\": " + jsonValue + "}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0L)]
+        [TestCase("1", 1L)]
+        [TestCase("-1", -1L)]
+        [TestCase("9223372036854775807", 9223372036854775807, Ignore = true, Reason = "Desired behaviour unclear")]
+        [TestCase("-9223372036854775808", -9223372036854775808, Ignore = true, Reason = "Desired behaviour unclear")]
+        public void NumberToInt64_Valid(string jsonValue, long expectedParsedValue)
+        {
+            string json = "{ \"singleInt64\": " + jsonValue + "}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleInt64);
+        }
+
+        // Assume that anything non-bounds-related is covered in the Int32 case
+        [Test]
+        [TestCase("-9223372036854775809", Ignore = true, Reason = "Desired behaviour unclear")]
+        [TestCase("9223372036854775808", Ignore = true, Reason = "Desired behaviour unclear")]
+        public void NumberToInt64_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleInt64\": " + jsonValue + "}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0UL)]
+        [TestCase("1", 1UL)]
+        [TestCase("18446744073709551615", 18446744073709551615, Ignore = true, Reason = "Desired behaviour unclear")]
+        public void NumberToUInt64_Valid(string jsonValue, ulong expectedParsedValue)
+        {
+            string json = "{ \"singleUint64\": " + jsonValue + "}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleUint64);
+        }
+
+        // Assume that anything non-bounds-related is covered in the Int32 case
+        [Test]
+        [TestCase("-1")]
+        [TestCase("18446744073709551616")]
+        public void NumberToUInt64_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleUint64\": " + jsonValue + "}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0d)]
+        [TestCase("1", 1d)]
+        [TestCase("1.000000", 1d)]
+        [TestCase("1.0000000000000000000000001", 1d)] // We don't notice that we haven't preserved the exact value
+        [TestCase("-1", -1d)]
+        [TestCase("1e1", 10d)]
+        [TestCase("1e01", 10d)] // Leading decimals are allowed in exponents
+        [TestCase("1E1", 10d)] // Either case is fine
+        [TestCase("-1e1", -10d)]
+        [TestCase("1.5e1", 15d)]
+        [TestCase("-1.5e1", -15d)]
+        [TestCase("15e-1", 1.5d)]
+        [TestCase("-15e-1", -1.5d)]
+        [TestCase("1.79769e308", 1.79769e308)]
+        [TestCase("-1.79769e308", -1.79769e308)]
+        public void NumberToDouble_Valid(string jsonValue, double expectedParsedValue)
+        {
+            string json = "{ \"singleDouble\": " + jsonValue + "}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleDouble);
+        }
+
+        [Test]
+        [TestCase("1.7977e308", Ignore = true, Reason = "Desired behaviour unclear")]
+        [TestCase("-1.7977e308", Ignore = true, Reason = "Desired behaviour unclear")]
+        [TestCase("1e309", Ignore = true, Reason = "Desired behaviour unclear")]
+        [TestCase("1,0")]
+        [TestCase("1.0.0")]
+        [TestCase("+1")]
+        [TestCase("00")]
+        [TestCase("--1")]
+        [TestCase("\u00BD")] // 1/2 as a single Unicode character. Just sanity checking...
+        public void NumberToDouble_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleDouble\": " + jsonValue + "}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        [Test]
+        [TestCase("0", 0f)]
+        [TestCase("1", 1f)]
+        [TestCase("1.000000", 1f)]
+        [TestCase("-1", -1f)]
+        [TestCase("3.402823e38", 3.402823e38f)]
+        [TestCase("-3.402823e38", -3.402823e38f)]
+        [TestCase("1.5e1", 15f)]
+        [TestCase("15e-1", 1.5f)]
+        public void NumberToFloat_Valid(string jsonValue, float expectedParsedValue)
+        {
+            string json = "{ \"singleFloat\": " + jsonValue + "}";
+            var parsed = TestAllTypes.Parser.ParseJson(json);
+            Assert.AreEqual(expectedParsedValue, parsed.SingleFloat);
+        }
+
+        [Test]
+        [TestCase("3.402824e38")]
+        [TestCase("-3.402824e38")]
+        [TestCase("1,0")]
+        [TestCase("1.0.0")]
+        [TestCase("+1")]
+        [TestCase("00")]
+        [TestCase("--1")]
+        public void NumberToFloat_Invalid(string jsonValue)
+        {
+            string json = "{ \"singleFloat\": " + jsonValue + "}";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+
+        // The simplest way of testing that the value has parsed correctly is to reformat it,
+        // as we trust the formatting. In many cases that will give the same result as the input,
+        // so in those cases we accept an expectedFormatted value of null. Sometimes the results
+        // will be different though, due to a different number of digits being provided.
+        [Test]
+        // Z offset
+        [TestCase("2015-10-09T14:46:23.123456789Z", null)]
+        [TestCase("2015-10-09T14:46:23.123456Z", null)]
+        [TestCase("2015-10-09T14:46:23.123Z", null)]
+        [TestCase("2015-10-09T14:46:23Z", null)]
+        [TestCase("2015-10-09T14:46:23.123456000Z", "2015-10-09T14:46:23.123456Z")]
+        [TestCase("2015-10-09T14:46:23.1234560Z", "2015-10-09T14:46:23.123456Z")]
+        [TestCase("2015-10-09T14:46:23.123000000Z", "2015-10-09T14:46:23.123Z")]
+        [TestCase("2015-10-09T14:46:23.1230Z", "2015-10-09T14:46:23.123Z")]
+        [TestCase("2015-10-09T14:46:23.00Z", "2015-10-09T14:46:23Z")]
+
+        // +00:00 offset
+        [TestCase("2015-10-09T14:46:23.123456789+00:00", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-09T14:46:23.123456+00:00", "2015-10-09T14:46:23.123456Z")]
+        [TestCase("2015-10-09T14:46:23.123+00:00", "2015-10-09T14:46:23.123Z")]
+        [TestCase("2015-10-09T14:46:23+00:00", "2015-10-09T14:46:23Z")]
+        [TestCase("2015-10-09T14:46:23.123456000+00:00", "2015-10-09T14:46:23.123456Z")]
+        [TestCase("2015-10-09T14:46:23.1234560+00:00", "2015-10-09T14:46:23.123456Z")]
+        [TestCase("2015-10-09T14:46:23.123000000+00:00", "2015-10-09T14:46:23.123Z")]
+        [TestCase("2015-10-09T14:46:23.1230+00:00", "2015-10-09T14:46:23.123Z")]
+        [TestCase("2015-10-09T14:46:23.00+00:00", "2015-10-09T14:46:23Z")]
+
+        // Other offsets (assume by now that the subsecond handling is okay)
+        [TestCase("2015-10-09T15:46:23.123456789+01:00", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-09T13:46:23.123456789-01:00", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-09T15:16:23.123456789+00:30", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-09T14:16:23.123456789-00:30", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-09T16:31:23.123456789+01:45", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-09T13:01:23.123456789-01:45", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-10T08:46:23.123456789+18:00", "2015-10-09T14:46:23.123456789Z")]
+        [TestCase("2015-10-08T20:46:23.123456789-18:00", "2015-10-09T14:46:23.123456789Z")]
+
+        // Leap years and min/max
+        [TestCase("2016-02-29T14:46:23.123456789Z", null)]
+        [TestCase("2000-02-29T14:46:23.123456789Z", null)]
+        [TestCase("0001-01-01T00:00:00Z", null)]
+        [TestCase("9999-12-31T23:59:59.999999999Z", null)]
+        public void Timestamp_Valid(string jsonValue, string expectedFormatted)
+        {
+            expectedFormatted = expectedFormatted ?? jsonValue;
+            string json = "\"" + jsonValue + "\"";
+            var parsed = Timestamp.Parser.ParseJson(json);
+            Assert.AreEqual(expectedFormatted, parsed.ToString());
+        }
+        
+        [Test]
+        [TestCase("2015-10-09 14:46:23.123456789Z", Description = "No T between date and time")]
+        [TestCase("2015/10/09T14:46:23.123456789Z", Description = "Wrong date separators")]
+        [TestCase("2015-10-09T14.46.23.123456789Z", Description = "Wrong time separators")]
+        [TestCase("2015-10-09T14:46:23,123456789Z", Description = "Wrong fractional second separators (valid ISO-8601 though)")]
+        [TestCase(" 2015-10-09T14:46:23.123456789Z", Description = "Whitespace at start")]
+        [TestCase("2015-10-09T14:46:23.123456789Z ", Description = "Whitespace at end")]
+        [TestCase("2015-10-09T14:46:23.1234567890", Description = "Too many digits")]
+        [TestCase("2015-10-09T14:46:23.123456789", Description = "No offset")]
+        [TestCase("2015-13-09T14:46:23.123456789Z", Description = "Invalid month")]
+        [TestCase("2015-10-32T14:46:23.123456789Z", Description = "Invalid day")]
+        [TestCase("2015-10-09T24:00:00.000000000Z", Description = "Invalid hour (valid ISO-8601 though)")]
+        [TestCase("2015-10-09T14:60:23.123456789Z", Description = "Invalid minutes")]
+        [TestCase("2015-10-09T14:46:60.123456789Z", Description = "Invalid seconds")]
+        [TestCase("2015-10-09T14:46:23.123456789+18:01", Description = "Offset too large (positive)")]
+        [TestCase("2015-10-09T14:46:23.123456789-18:01", Description = "Offset too large (negative)")]
+        [TestCase("2015-10-09T14:46:23.123456789-00:00", Description = "Local offset (-00:00) makes no sense here")]
+        [TestCase("0001-01-01T00:00:00+00:01", Description = "Value before earliest when offset applied")]
+        [TestCase("9999-12-31T23:59:59.999999999-00:01", Description = "Value after latest when offset applied")]
+        [TestCase("2100-02-29T14:46:23.123456789Z", Description = "Feb 29th on a non-leap-year")]
+        public void Timestamp_Invalid(string jsonValue)
+        {
+            string json = "\"" + jsonValue + "\"";
+            Assert.Throws<InvalidProtocolBufferException>(() => Timestamp.Parser.ParseJson(json));
+        }
+
+        [Test]
+        public void StructValue_Null()
+        {
+            Assert.AreEqual(new Value { NullValue = 0 }, Value.Parser.ParseJson("null"));
+        }
+
+        [Test]
+        public void StructValue_String()
+        {
+            Assert.AreEqual(new Value { StringValue = "hi" }, Value.Parser.ParseJson("\"hi\""));
+        }
+
+        [Test]
+        public void StructValue_Bool()
+        {
+            Assert.AreEqual(new Value { BoolValue = true }, Value.Parser.ParseJson("true"));
+            Assert.AreEqual(new Value { BoolValue = false }, Value.Parser.ParseJson("false"));
+        }
+
+        [Test]
+        public void StructValue_List()
+        {
+            Assert.AreEqual(Value.ForList(Value.ForNumber(1), Value.ForString("x")), Value.Parser.ParseJson("[1, \"x\"]"));
+        }
+
+        [Test]
+        public void ParseListValue()
+        {
+            Assert.AreEqual(new ListValue { Values = { Value.ForNumber(1), Value.ForString("x") } }, ListValue.Parser.ParseJson("[1, \"x\"]"));
+        }
+
+        [Test]
+        public void StructValue_Struct()
+        {
+            Assert.AreEqual(
+                Value.ForStruct(new Struct { Fields = { { "x", Value.ForNumber(1) }, { "y", Value.ForString("z") } } }),
+                Value.Parser.ParseJson("{ \"x\": 1, \"y\": \"z\" }"));
+        }
+
+        [Test]
+        public void ParseStruct()
+        {
+            Assert.AreEqual(new Struct { Fields = { { "x", Value.ForNumber(1) }, { "y", Value.ForString("z") } } },
+                Struct.Parser.ParseJson("{ \"x\": 1, \"y\": \"z\" }"));
+        }
+
+        // TODO for duration parsing: upper and lower bounds.
+        // +/- 315576000000 seconds
+
+        [Test]
+        [TestCase("1.123456789s", null)]
+        [TestCase("1.123456s", null)]
+        [TestCase("1.123s", null)]
+        [TestCase("1.12300s", "1.123s")]
+        [TestCase("1.12345s", "1.123450s")]
+        [TestCase("1s", null)]
+        [TestCase("-1.123456789s", null)]
+        [TestCase("-1.123456s", null)]
+        [TestCase("-1.123s", null)]
+        [TestCase("-1s", null)]
+        [TestCase("0.123s", null)]
+        [TestCase("-0.123s", null)]
+        [TestCase("123456.123s", null)]
+        [TestCase("-123456.123s", null)]
+        // Upper and lower bounds
+        [TestCase("315576000000s", null)]
+        [TestCase("-315576000000s", null)]
+        public void Duration_Valid(string jsonValue, string expectedFormatted)
+        {
+            expectedFormatted = expectedFormatted ?? jsonValue;
+            string json = "\"" + jsonValue + "\"";
+            var parsed = Duration.Parser.ParseJson(json);
+            Assert.AreEqual(expectedFormatted, parsed.ToString());
+        }
+
+        // The simplest way of testing that the value has parsed correctly is to reformat it,
+        // as we trust the formatting. In many cases that will give the same result as the input,
+        // so in those cases we accept an expectedFormatted value of null. Sometimes the results
+        // will be different though, due to a different number of digits being provided.
+        [Test]
+        [TestCase("1.1234567890s", Description = "Too many digits")]
+        [TestCase("1.123456789", Description = "No suffix")]
+        [TestCase("1.123456789ss", Description = "Too much suffix")]
+        [TestCase("1.123456789S", Description = "Upper case suffix")]
+        [TestCase("+1.123456789s", Description = "Leading +")]
+        [TestCase(".123456789s", Description = "No integer before the fraction")]
+        [TestCase("1,123456789s", Description = "Comma as decimal separator")]
+        [TestCase("1x1.123456789s", Description = "Non-digit in integer part")]
+        [TestCase("1.1x3456789s", Description = "Non-digit in fractional part")]
+        [TestCase(" 1.123456789s", Description = "Whitespace before fraction")]
+        [TestCase("1.123456789s ", Description = "Whitespace after value")]
+        [TestCase("01.123456789s", Description = "Leading zero (positive)")]
+        [TestCase("-01.123456789s", Description = "Leading zero (negative)")]
+        [TestCase("--0.123456789s", Description = "Double minus sign")]
+        // Violate upper/lower bounds in various ways
+        [TestCase("315576000001s", Description = "Integer part too large")]
+        [TestCase("315576000000.000000001s", Description = "Integer part is upper bound; non-zero fraction")]
+        [TestCase("3155760000000s", Description = "Integer part too long (positive)")]
+        [TestCase("-3155760000000s", Description = "Integer part too long (negative)")]
+        public void Duration_Invalid(string jsonValue)
+        {
+            string json = "\"" + jsonValue + "\"";
+            Assert.Throws<InvalidProtocolBufferException>(() => Duration.Parser.ParseJson(json));
+        }
+
+        // Not as many tests for field masks as I'd like; more to be added when we have more
+        // detailed specifications.
+
+        [Test]
+        [TestCase("")]
+        [TestCase("foo", "foo")]
+        [TestCase("foo,bar", "foo", "bar")]
+        [TestCase("foo.bar", "foo.bar")]
+        [TestCase("fooBar", "foo_bar")]
+        [TestCase("fooBar.bazQux", "foo_bar.baz_qux")]
+        public void FieldMask_Valid(string jsonValue, params string[] expectedPaths)
+        {
+            string json = "\"" + jsonValue + "\"";
+            var parsed = FieldMask.Parser.ParseJson(json);
+            CollectionAssert.AreEqual(expectedPaths, parsed.Paths);
+        }
+
+        [Test]
+        public void DataAfterObject()
+        {
+            string json = "{} 10";
+            Assert.Throws<InvalidProtocolBufferException>(() => TestAllTypes.Parser.ParseJson(json));
+        }
+    }
+}
diff --git a/csharp/src/Google.Protobuf.Test/JsonTokenizerTest.cs b/csharp/src/Google.Protobuf.Test/JsonTokenizerTest.cs
new file mode 100644
index 0000000..868d9f7
--- /dev/null
+++ b/csharp/src/Google.Protobuf.Test/JsonTokenizerTest.cs
@@ -0,0 +1,352 @@
+﻿#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+using NUnit.Framework;
+using System;
+using System.IO;
+
+namespace Google.Protobuf
+{
+    public class JsonTokenizerTest
+    {
+        [Test]
+        public void EmptyObjectValue()
+        {
+            AssertTokens("{}", JsonToken.StartObject, JsonToken.EndObject);
+        }
+
+        [Test]
+        public void EmptyArrayValue()
+        {
+            AssertTokens("[]", JsonToken.StartArray, JsonToken.EndArray);
+        }
+
+        [Test]
+        [TestCase("foo", "foo")]
+        [TestCase("tab\\t", "tab\t")]
+        [TestCase("line\\nfeed", "line\nfeed")]
+        [TestCase("carriage\\rreturn", "carriage\rreturn")]
+        [TestCase("back\\bspace", "back\bspace")]
+        [TestCase("form\\ffeed", "form\ffeed")]
+        [TestCase("escaped\\/slash", "escaped/slash")]
+        [TestCase("escaped\\\\backslash", "escaped\\backslash")]
+        [TestCase("escaped\\\"quote", "escaped\"quote")]
+        [TestCase("foo {}[] bar", "foo {}[] bar")]
+        [TestCase("foo\\u09aFbar", "foo\u09afbar")] // Digits, upper hex, lower hex
+        [TestCase("ab\ud800\udc00cd", "ab\ud800\udc00cd")]
+        [TestCase("ab\\ud800\\udc00cd", "ab\ud800\udc00cd")]
+        public void StringValue(string json, string expectedValue)
+        {
+            AssertTokensNoReplacement("\"" + json + "\"", JsonToken.Value(expectedValue));
+        }
+
+        // Valid surrogate pairs, with mixed escaping. These test cases can't be expressed
+        // using TestCase as they have no valid UTF-8 representation.
+        // It's unclear exactly how we should handle a mixture of escaped or not: that can't
+        // come from UTF-8 text, but could come from a .NET string. For the moment,
+        // treat it as valid in the obvious way.
+        [Test]
+        public void MixedSurrogatePairs()
+        {
+            string expected = "\ud800\udc00";
+            AssertTokens("'\\ud800\udc00'", JsonToken.Value(expected));
+            AssertTokens("'\ud800\\udc00'", JsonToken.Value(expected));
+        }
+
+        [Test]
+        [TestCase("embedded tab\t")]
+        [TestCase("embedded CR\r")]
+        [TestCase("embedded LF\n")]
+        [TestCase("embedded bell\u0007")]
+        [TestCase("bad escape\\a")]
+        [TestCase("incomplete escape\\")]
+        [TestCase("incomplete Unicode escape\\u000")]
+        [TestCase("invalid Unicode escape\\u000H")]
+        // Surrogate pair handling, both in raw .NET strings and escaped. We only need
+        // to detect this in strings, as non-ASCII characters anywhere other than in strings
+        // will already lead to parsing errors.
+        [TestCase("\\ud800")]
+        [TestCase("\\udc00")]
+        [TestCase("\\ud800x")]
+        [TestCase("\\udc00x")]
+        [TestCase("\\udc00\\ud800y")]
+        public void InvalidStringValue(string json)
+        {
+            AssertThrowsAfter("\"" + json + "\"");
+        }
+
+        // Tests for invalid strings that can't be expressed in attributes,
+        // as the constants can't be expressed as UTF-8 strings.
+        [Test]
+        public void InvalidSurrogatePairs()
+        {
+            AssertThrowsAfter("\"\ud800x\"");
+            AssertThrowsAfter("\"\udc00y\"");
+            AssertThrowsAfter("\"\udc00\ud800y\"");
+        }
+
+        [Test]
+        [TestCase("0", 0)]
+        [TestCase("-0", 0)] // We don't distinguish between positive and negative 0
+        [TestCase("1", 1)]
+        [TestCase("-1", -1)]
+        // From here on, assume leading sign is okay...
+        [TestCase("1.125", 1.125)]
+        [TestCase("1.0", 1)]
+        [TestCase("1e5", 100000)]
+        [TestCase("1e000000", 1)] // Weird, but not prohibited by the spec
+        [TestCase("1E5", 100000)]
+        [TestCase("1e+5", 100000)]
+        [TestCase("1E-5", 0.00001)]
+        [TestCase("123E-2", 1.23)]
+        [TestCase("123.45E3", 123450)]
+        [TestCase("   1   ", 1)]
+        public void NumberValue(string json, double expectedValue)
+        {
+            AssertTokens(json, JsonToken.Value(expectedValue));
+        }
+
+        [Test]
+        [TestCase("00")]
+        [TestCase(".5")]
+        [TestCase("1.")]
+        [TestCase("1e")]
+        [TestCase("1e-")]
+        [TestCase("--")]
+        [TestCase("--1")]
+        [TestCase("-1.7977e308")]
+        [TestCase("1.7977e308")]
+        public void InvalidNumberValue(string json)
+        {
+            AssertThrowsAfter(json);
+        }
+
+        [Test]
+        [TestCase("nul")]
+        [TestCase("nothing")]
+        [TestCase("truth")]
+        [TestCase("fALSEhood")]
+        public void InvalidLiterals(string json)
+        {
+            AssertThrowsAfter(json);
+        }
+
+        [Test]
+        public void NullValue()
+        {
+            AssertTokens("null", JsonToken.Null);
+        }
+
+        [Test]
+        public void TrueValue()
+        {
+            AssertTokens("true", JsonToken.True);
+        }
+
+        [Test]
+        public void FalseValue()
+        {
+            AssertTokens("false", JsonToken.False);
+        }
+
+        [Test]
+        public void SimpleObject()
+        {
+            AssertTokens("{'x': 'y'}",
+                JsonToken.StartObject, JsonToken.Name("x"), JsonToken.Value("y"), JsonToken.EndObject);
+        }
+        
+        [Test]
+        [TestCase("[10, 20", 3)]
+        [TestCase("[10,", 2)]
+        [TestCase("[10:20]", 2)]
+        [TestCase("[", 1)]
+        [TestCase("[,", 1)]
+        [TestCase("{", 1)]
+        [TestCase("{,", 1)]
+        [TestCase("{", 1)]
+        [TestCase("{[", 1)]
+        [TestCase("{{", 1)]
+        [TestCase("{0", 1)]
+        [TestCase("{null", 1)]
+        [TestCase("{false", 1)]
+        [TestCase("{true", 1)]
+        [TestCase("}", 0)]
+        [TestCase("]", 0)]
+        [TestCase(",", 0)]
+        [TestCase("'foo' 'bar'", 1)]
+        [TestCase(":", 0)]
+        [TestCase("'foo", 0)] // Incomplete string
+        [TestCase("{ 'foo' }", 2)]
+        [TestCase("{ x:1", 1)] // Property names must be quoted
+        [TestCase("{]", 1)]
+        [TestCase("[}", 1)]
+        [TestCase("[1,", 2)]
+        [TestCase("{'x':0]", 3)]
+        [TestCase("{ 'foo': }", 2)]
+        [TestCase("{ 'foo':'bar', }", 3)]
+        public void InvalidStructure(string json, int expectedValidTokens)
+        {
+            // Note: we don't test that the earlier tokens are exactly as expected,
+            // partly because that's hard to parameterize.
+            var reader = new StringReader(json.Replace('\'', '"'));
+            var tokenizer = new JsonTokenizer(reader);
+            for (int i = 0; i < expectedValidTokens; i++)
+            {
+                Assert.IsNotNull(tokenizer.Next());
+            }
+            Assert.Throws<InvalidProtocolBufferException>(() => tokenizer.Next());
+        }
+
+        [Test]
+        public void ArrayMixedType()
+        {
+            AssertTokens("[1, 'foo', null, false, true, [2], {'x':'y' }]",
+                JsonToken.StartArray,
+                JsonToken.Value(1),
+                JsonToken.Value("foo"),
+                JsonToken.Null,
+                JsonToken.False,
+                JsonToken.True,
+                JsonToken.StartArray,
+                JsonToken.Value(2),
+                JsonToken.EndArray,
+                JsonToken.StartObject,
+                JsonToken.Name("x"),
+                JsonToken.Value("y"),
+                JsonToken.EndObject,
+                JsonToken.EndArray);
+        }
+
+        [Test]
+        public void ObjectMixedType()
+        {
+            AssertTokens(@"{'a': 1, 'b': 'bar', 'c': null, 'd': false, 'e': true, 
+                           'f': [2], 'g': {'x':'y' }}",
+                JsonToken.StartObject,
+                JsonToken.Name("a"),
+                JsonToken.Value(1),
+                JsonToken.Name("b"),
+                JsonToken.Value("bar"),
+                JsonToken.Name("c"),
+                JsonToken.Null,
+                JsonToken.Name("d"),
+                JsonToken.False,
+                JsonToken.Name("e"),
+                JsonToken.True,
+                JsonToken.Name("f"),
+                JsonToken.StartArray,
+                JsonToken.Value(2),
+                JsonToken.EndArray,
+                JsonToken.Name("g"),
+                JsonToken.StartObject,
+                JsonToken.Name("x"),
+                JsonToken.Value("y"),
+                JsonToken.EndObject,
+                JsonToken.EndObject);
+        }
+
+        [Test]
+        public void NextAfterEndDocumentThrows()
+        {
+            var tokenizer = new JsonTokenizer(new StringReader("null"));
+            Assert.AreEqual(JsonToken.Null, tokenizer.Next());
+            Assert.AreEqual(JsonToken.EndDocument, tokenizer.Next());
+            Assert.Throws<InvalidOperationException>(() => tokenizer.Next());
+        }
+
+        [Test]
+        public void CanPushBackEndDocument()
+        {
+            var tokenizer = new JsonTokenizer(new StringReader("null"));
+            Assert.AreEqual(JsonToken.Null, tokenizer.Next());
+            Assert.AreEqual(JsonToken.EndDocument, tokenizer.Next());
+            tokenizer.PushBack(JsonToken.EndDocument);
+            Assert.AreEqual(JsonToken.EndDocument, tokenizer.Next());
+            Assert.Throws<InvalidOperationException>(() => tokenizer.Next());
+        }
+       
+        /// <summary>
+        /// Asserts that the specified JSON is tokenized into the given sequence of tokens.
+        /// All apostrophes are first converted to double quotes, allowing any tests
+        /// that don't need to check actual apostrophe handling to use apostrophes in the JSON, avoiding
+        /// messy string literal escaping. The "end document" token is not specified in the list of 
+        /// expected tokens, but is implicit.
+        /// </summary>
+        private static void AssertTokens(string json, params JsonToken[] expectedTokens)
+        {
+            AssertTokensNoReplacement(json.Replace('\'', '"'), expectedTokens);
+        }
+
+        /// <summary>
+        /// Asserts that the specified JSON is tokenized into the given sequence of tokens.
+        /// Unlike <see cref="AssertTokens(string, JsonToken[])"/>, this does not perform any character
+        /// replacement on the specified JSON, and should be used when the text contains apostrophes which
+        /// are expected to be used *as* apostrophes. The "end document" token is not specified in the list of 
+        /// expected tokens, but is implicit.
+        /// </summary>
+        private static void AssertTokensNoReplacement(string json, params JsonToken[] expectedTokens)
+        {
+            var reader = new StringReader(json);
+            var tokenizer = new JsonTokenizer(reader);
+            for (int i = 0; i < expectedTokens.Length; i++)
+            {
+                var actualToken = tokenizer.Next();
+                if (actualToken == JsonToken.EndDocument)
+                {
+                    Assert.Fail("Expected {0} but reached end of token stream", expectedTokens[i]);
+                }
+                Assert.AreEqual(expectedTokens[i], actualToken);
+            }
+            var finalToken = tokenizer.Next();
+            if (finalToken != JsonToken.EndDocument)
+            {
+                Assert.Fail("Expected token stream to be exhausted; received {0}", finalToken);
+            }
+        }
+
+        private static void AssertThrowsAfter(string json, params JsonToken[] expectedTokens)
+        {
+            var reader = new StringReader(json);
+            var tokenizer = new JsonTokenizer(reader);
+            for (int i = 0; i < expectedTokens.Length; i++)
+            {
+                var actualToken = tokenizer.Next();
+                if (actualToken == JsonToken.EndDocument)
+                {
+                    Assert.Fail("Expected {0} but reached end of document", expectedTokens[i]);
+                }
+                Assert.AreEqual(expectedTokens[i], actualToken);
+            }
+            Assert.Throws<InvalidProtocolBufferException>(() => tokenizer.Next());
+        }
+    }
+}
diff --git a/csharp/src/Google.Protobuf/FieldCodec.cs b/csharp/src/Google.Protobuf/FieldCodec.cs
index 20a1f43..54cbc20 100644
--- a/csharp/src/Google.Protobuf/FieldCodec.cs
+++ b/csharp/src/Google.Protobuf/FieldCodec.cs
@@ -30,6 +30,7 @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #endregion
 
+using Google.Protobuf.WellKnownTypes;
 using System;
 using System.Collections.Generic;
 
@@ -261,20 +262,17 @@
         /// </remarks>
         private static class WrapperCodecs
         {
-            // All the field numbers are the same (1).
-            private const int WrapperValueFieldNumber = Google.Protobuf.WellKnownTypes.Int32Value.ValueFieldNumber;
-
-            private static readonly Dictionary<Type, object> Codecs = new Dictionary<Type, object>
+            private static readonly Dictionary<System.Type, object> Codecs = new Dictionary<System.Type, object>
             {
-                { typeof(bool), ForBool(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
-                { typeof(int), ForInt32(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
-                { typeof(long), ForInt64(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
-                { typeof(uint), ForUInt32(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
-                { typeof(ulong), ForUInt64(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
-                { typeof(float), ForFloat(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Fixed32)) },
-                { typeof(double), ForDouble(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.Fixed64)) },
-                { typeof(string), ForString(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.LengthDelimited)) },
-                { typeof(ByteString), ForBytes(WireFormat.MakeTag(WrapperValueFieldNumber, WireFormat.WireType.LengthDelimited)) }
+                { typeof(bool), ForBool(WireFormat.MakeTag(Wrappers.WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
+                { typeof(int), ForInt32(WireFormat.MakeTag(Wrappers.WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
+                { typeof(long), ForInt64(WireFormat.MakeTag(Wrappers.WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
+                { typeof(uint), ForUInt32(WireFormat.MakeTag(Wrappers.WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
+                { typeof(ulong), ForUInt64(WireFormat.MakeTag(Wrappers.WrapperValueFieldNumber, WireFormat.WireType.Varint)) },
+                { typeof(float), ForFloat(WireFormat.MakeTag(Wrappers.WrapperValueFieldNumber, WireFormat.WireType.Fixed32)) },
+                { typeof(double), ForDouble(WireFormat.MakeTag(Wrappers.WrapperValueFieldNumber, WireFormat.WireType.Fixed64)) },
+                { typeof(string), ForString(WireFormat.MakeTag(Wrappers.WrapperValueFieldNumber, WireFormat.WireType.LengthDelimited)) },
+                { typeof(ByteString), ForBytes(WireFormat.MakeTag(Wrappers.WrapperValueFieldNumber, WireFormat.WireType.LengthDelimited)) }
             };
 
             /// <summary>
diff --git a/csharp/src/Google.Protobuf/Google.Protobuf.csproj b/csharp/src/Google.Protobuf/Google.Protobuf.csproj
index 8c680d4..0039943 100644
--- a/csharp/src/Google.Protobuf/Google.Protobuf.csproj
+++ b/csharp/src/Google.Protobuf/Google.Protobuf.csproj
@@ -85,6 +85,9 @@
     <Compile Include="FrameworkPortability.cs" />
     <Compile Include="IDeepCloneable.cs" />
     <Compile Include="JsonFormatter.cs" />
+    <Compile Include="JsonParser.cs" />
+    <Compile Include="JsonToken.cs" />
+    <Compile Include="JsonTokenizer.cs" />
     <Compile Include="MessageExtensions.cs" />
     <Compile Include="IMessage.cs" />
     <Compile Include="InvalidProtocolBufferException.cs" />
@@ -130,7 +133,9 @@
     <Compile Include="WellKnownTypes\Timestamp.cs" />
     <Compile Include="WellKnownTypes\TimestampPartial.cs" />
     <Compile Include="WellKnownTypes\Type.cs" />
+    <Compile Include="WellKnownTypes\ValuePartial.cs" />
     <Compile Include="WellKnownTypes\Wrappers.cs" />
+    <Compile Include="WellKnownTypes\WrappersPartial.cs" />
     <Compile Include="WireFormat.cs" />
   </ItemGroup>
   <ItemGroup>
diff --git a/csharp/src/Google.Protobuf/JsonFormatter.cs b/csharp/src/Google.Protobuf/JsonFormatter.cs
index 3f9bd47..2070f62 100644
--- a/csharp/src/Google.Protobuf/JsonFormatter.cs
+++ b/csharp/src/Google.Protobuf/JsonFormatter.cs
@@ -189,6 +189,7 @@
         }
 
         // Converted from src/google/protobuf/util/internal/utility.cc ToCamelCase
+        // TODO: Use the new field in FieldDescriptor.
         internal static string ToCamelCase(string input)
         {
             bool capitalizeNext = false;
@@ -382,10 +383,19 @@
                 WriteNull(builder);
                 return;
             }
-            // For wrapper types, the value will be the (possibly boxed) "native" value,
-            // so we can write it as if we were unconditionally writing the Value field for the wrapper type.
+            // For wrapper types, the value will either be the (possibly boxed) "native" value,
+            // or the message itself if we're formatting it at the top level (e.g. just calling ToString on the object itself).
+            // If it's the message form, we can extract the value first, which *will* be the (possibly boxed) native value,
+            // and then proceed, writing it as if we were definitely in a field. (We never need to wrap it in an extra string...
+            // WriteValue will do the right thing.)
+            // TODO: Detect this differently when we have dynamic messages.
             if (descriptor.File == Int32Value.Descriptor.File)
             {
+                if (value is IMessage)
+                {
+                    var message = (IMessage) value;
+                    value = message.Descriptor.Fields[Wrappers.WrapperValueFieldNumber].Accessor.GetValue(message);
+                }
                 WriteValue(builder, value);
                 return;
             }
@@ -750,7 +760,6 @@
 
             private readonly bool formatDefaultValues;
 
-
             /// <summary>
             /// Whether fields whose values are the default for the field type (e.g. 0 for integers)
             /// should be formatted (true) or omitted (false).
diff --git a/csharp/src/Google.Protobuf/JsonParser.cs b/csharp/src/Google.Protobuf/JsonParser.cs
new file mode 100644
index 0000000..6d2638d
--- /dev/null
+++ b/csharp/src/Google.Protobuf/JsonParser.cs
@@ -0,0 +1,813 @@
+﻿#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+using Google.Protobuf.Reflection;
+using Google.Protobuf.WellKnownTypes;
+using System;
+using System.Collections;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using System.Text;
+using System.Text.RegularExpressions;
+
+namespace Google.Protobuf
+{
+    /// <summary>
+    /// Reflection-based converter from JSON to messages.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// Instances of this class are thread-safe, with no mutable state.
+    /// </para>
+    /// <para>
+    /// This is a simple start to get JSON parsing working. As it's reflection-based,
+    /// it's not as quick as baking calls into generated messages - but is a simpler implementation.
+    /// (This code is generally not heavily optimized.)
+    /// </para>
+    /// </remarks>
+    public sealed class JsonParser
+    {
+        // Note: using 0-9 instead of \d to ensure no non-ASCII digits.
+        // This regex isn't a complete validator, but will remove *most* invalid input. We rely on parsing to do the rest.
+        private static readonly Regex TimestampRegex = new Regex(@"^(?<datetime>[0-9]{4}-[01][0-9]-[0-3][0-9]T[012][0-9]:[0-5][0-9]:[0-5][0-9])(?<subseconds>\.[0-9]{1,9})?(?<offset>(Z|[+-][0-1][0-9]:[0-5][0-9]))$", FrameworkPortability.CompiledRegexWhereAvailable);
+        private static readonly Regex DurationRegex = new Regex(@"^(?<sign>-)?(?<int>[0-9]{1,12})(?<subseconds>\.[0-9]{1,9})?s$", FrameworkPortability.CompiledRegexWhereAvailable);
+        private static readonly int[] SubsecondScalingFactors = { 0, 100000000, 100000000, 10000000, 1000000, 100000, 10000, 1000, 100, 10, 1 };
+        private static readonly char[] FieldMaskPathSeparators = new[] { ',' };
+
+        private static readonly JsonParser defaultInstance = new JsonParser(Settings.Default);
+
+        private static readonly Dictionary<string, Action<JsonParser, IMessage, JsonTokenizer>>
+            WellKnownTypeHandlers = new Dictionary<string, Action<JsonParser, IMessage, JsonTokenizer>>
+        {
+            { Timestamp.Descriptor.FullName, (parser, message, tokenizer) => MergeTimestamp(message, tokenizer.Next()) },
+            { Duration.Descriptor.FullName, (parser, message, tokenizer) => MergeDuration(message, tokenizer.Next()) },
+            { Value.Descriptor.FullName, (parser, message, tokenizer) => parser.MergeStructValue(message, tokenizer) },
+            { ListValue.Descriptor.FullName, (parser, message, tokenizer) => parser.MergeRepeatedField(message, message.Descriptor.Fields[ListValue.ValuesFieldNumber], tokenizer) },
+            { Struct.Descriptor.FullName, (parser, message, tokenizer) => parser.MergeStruct(message, tokenizer) },
+            { FieldMask.Descriptor.FullName, (parser, message, tokenizer) => MergeFieldMask(message, tokenizer.Next()) },
+            { Int32Value.Descriptor.FullName, MergeWrapperField },
+            { Int64Value.Descriptor.FullName, MergeWrapperField },
+            { UInt32Value.Descriptor.FullName, MergeWrapperField },
+            { UInt64Value.Descriptor.FullName, MergeWrapperField },
+            { FloatValue.Descriptor.FullName, MergeWrapperField },
+            { DoubleValue.Descriptor.FullName, MergeWrapperField },
+            { BytesValue.Descriptor.FullName, MergeWrapperField },
+            { StringValue.Descriptor.FullName, MergeWrapperField }
+        };
+
+        // Convenience method to avoid having to repeat the same code multiple times in the above
+        // dictionary initialization.
+        private static void MergeWrapperField(JsonParser parser, IMessage message, JsonTokenizer tokenizer)
+        {
+            parser.MergeField(message, message.Descriptor.Fields[Wrappers.WrapperValueFieldNumber], tokenizer);
+        }
+
+        /// <summary>
+        /// Returns a formatter using the default settings.        /// </summary>
+        public static JsonParser Default { get { return defaultInstance; } }
+
+// Currently the settings are unused.
+// TODO: When we've implemented Any (and the json spec is finalized), revisit whether they're
+// needed at all.
+#pragma warning disable 0414
+        private readonly Settings settings;
+#pragma warning restore 0414
+
+        /// <summary>
+        /// Creates a new formatted with the given settings.
+        /// </summary>
+        /// <param name="settings">The settings.</param>
+        public JsonParser(Settings settings)
+        {
+            this.settings = settings;
+        }
+
+        /// <summary>
+        /// Parses <paramref name="json"/> and merges the information into the given message.
+        /// </summary>
+        /// <param name="message">The message to merge the JSON information into.</param>
+        /// <param name="json">The JSON to parse.</param>
+        internal void Merge(IMessage message, string json)
+        {
+            Merge(message, new StringReader(json));
+        }
+
+        /// <summary>
+        /// Parses JSON read from <paramref name="jsonReader"/> and merges the information into the given message.
+        /// </summary>
+        /// <param name="message">The message to merge the JSON information into.</param>
+        /// <param name="jsonReader">Reader providing the JSON to parse.</param>
+        internal void Merge(IMessage message, TextReader jsonReader)
+        {
+            var tokenizer = new JsonTokenizer(jsonReader);
+            Merge(message, tokenizer);
+            var lastToken = tokenizer.Next();
+            if (lastToken != JsonToken.EndDocument)
+            {
+                throw new InvalidProtocolBufferException("Expected end of JSON after object");
+            }
+        }
+
+        /// <summary>
+        /// Merges the given message using data from the given tokenizer. In most cases, the next
+        /// token should be a "start object" token, but wrapper types and nullity can invalidate
+        /// that assumption. This is implemented as an LL(1) recursive descent parser over the stream
+        /// of tokens provided by the tokenizer. This token stream is assumed to be valid JSON, with the
+        /// tokenizer performing that validation - but not every token stream is valid "protobuf JSON".
+        /// </summary>
+        private void Merge(IMessage message, JsonTokenizer tokenizer)
+        {
+            if (message.Descriptor.IsWellKnownType)
+            {
+                Action<JsonParser, IMessage, JsonTokenizer> handler;
+                if (WellKnownTypeHandlers.TryGetValue(message.Descriptor.FullName, out handler))
+                {
+                    handler(this, message, tokenizer);
+                    return;
+                }
+                // Well-known types with no special handling continue in the normal way.
+            }
+            var token = tokenizer.Next();
+            if (token.Type != JsonToken.TokenType.StartObject)
+            {
+                throw new InvalidProtocolBufferException("Expected an object");
+            }
+            var descriptor = message.Descriptor;
+            // TODO: Make this more efficient, e.g. by building it once in the descriptor.
+            // Additionally, we need to consider whether to parse field names in their original proto form,
+            // and any overrides in the descriptor. But yes, all of this should be in the descriptor somehow...
+            // the descriptor can expose the dictionary.
+            var jsonFieldMap = descriptor.Fields.InDeclarationOrder().ToDictionary(field => JsonFormatter.ToCamelCase(field.Name));
+            while (true)
+            {
+                token = tokenizer.Next();
+                if (token.Type == JsonToken.TokenType.EndObject)
+                {
+                    return;
+                }
+                if (token.Type != JsonToken.TokenType.Name)
+                {
+                    throw new InvalidOperationException("Unexpected token type " + token.Type);
+                }
+                string name = token.StringValue;
+                FieldDescriptor field;
+                if (jsonFieldMap.TryGetValue(name, out field))
+                {
+                    MergeField(message, field, tokenizer);
+                }
+                else
+                {
+                    // TODO: Is this what we want to do? If not, we'll need to skip the value,
+                    // which may be an object or array. (We might want to put code in the tokenizer
+                    // to do that.)
+                    throw new InvalidProtocolBufferException("Unknown field: " + name);
+                }
+            }
+        }
+
+        private void MergeField(IMessage message, FieldDescriptor field, JsonTokenizer tokenizer)
+        {
+            var token = tokenizer.Next();
+            if (token.Type == JsonToken.TokenType.Null)
+            {
+                // Note: different from Java API, which just ignores it.
+                // TODO: Bring it more in line? Discuss...
+                field.Accessor.Clear(message);
+                return;
+            }
+            tokenizer.PushBack(token);
+
+            if (field.IsMap)
+            {
+                MergeMapField(message, field, tokenizer);
+            }
+            else if (field.IsRepeated)
+            {
+                MergeRepeatedField(message, field, tokenizer);
+            }
+            else
+            {
+                var value = ParseSingleValue(field, tokenizer);
+                field.Accessor.SetValue(message, value);
+            }
+        }
+
+        private void MergeRepeatedField(IMessage message, FieldDescriptor field, JsonTokenizer tokenizer)
+        {
+            var token = tokenizer.Next();
+            if (token.Type != JsonToken.TokenType.StartArray)
+            {
+                throw new InvalidProtocolBufferException("Repeated field value was not an array. Token type: " + token.Type);
+            }
+
+            IList list = (IList) field.Accessor.GetValue(message);
+            while (true)
+            {
+                token = tokenizer.Next();
+                if (token.Type == JsonToken.TokenType.EndArray)
+                {
+                    return;
+                }
+                tokenizer.PushBack(token);
+                list.Add(ParseSingleValue(field, tokenizer));
+            }
+        }
+
+        private void MergeMapField(IMessage message, FieldDescriptor field, JsonTokenizer tokenizer)
+        {
+            // Map fields are always objects, even if the values are well-known types: ParseSingleValue handles those.
+            var token = tokenizer.Next();
+            if (token.Type != JsonToken.TokenType.StartObject)
+            {
+                throw new InvalidProtocolBufferException("Expected an object to populate a map");
+            }
+
+            var type = field.MessageType;
+            var keyField = type.FindFieldByNumber(1);
+            var valueField = type.FindFieldByNumber(2);
+            if (keyField == null || valueField == null)
+            {
+                throw new InvalidProtocolBufferException("Invalid map field: " + field.FullName);
+            }
+            IDictionary dictionary = (IDictionary) field.Accessor.GetValue(message);
+
+            while (true)
+            {
+                token = tokenizer.Next();
+                if (token.Type == JsonToken.TokenType.EndObject)
+                {
+                    return;
+                }
+                object key = ParseMapKey(keyField, token.StringValue);
+                object value = ParseSingleValue(valueField, tokenizer);
+                // TODO: Null handling
+                dictionary[key] = value;
+            }
+        }
+
+        private object ParseSingleValue(FieldDescriptor field, JsonTokenizer tokenizer)
+        {
+            var token = tokenizer.Next();
+            if (token.Type == JsonToken.TokenType.Null)
+            {
+                if (field.FieldType == FieldType.Message && field.MessageType.FullName == Value.Descriptor.FullName)
+                {
+                    return new Value { NullValue = NullValue.NULL_VALUE };
+                }
+                return null;
+            }
+
+            var fieldType = field.FieldType;
+            if (fieldType == FieldType.Message)
+            {
+                // Parse wrapper types as their constituent types.
+                // TODO: What does this mean for null?
+                // TODO: Detect this differently when we have dynamic messages, and put it in one place...
+                if (field.MessageType.IsWellKnownType && field.MessageType.File == Int32Value.Descriptor.File)
+                {
+                    field = field.MessageType.Fields[Wrappers.WrapperValueFieldNumber];
+                    fieldType = field.FieldType;
+                }
+                else
+                {
+                    // TODO: Merge the current value in message? (Public API currently doesn't make this relevant as we don't expose merging.)
+                    tokenizer.PushBack(token);
+                    IMessage subMessage = NewMessageForField(field);
+                    Merge(subMessage, tokenizer);
+                    return subMessage;
+                }
+            }
+
+            switch (token.Type)
+            {
+                case JsonToken.TokenType.True:
+                case JsonToken.TokenType.False:
+                    if (fieldType == FieldType.Bool)
+                    {
+                        return token.Type == JsonToken.TokenType.True;
+                    }
+                    // Fall through to "we don't support this type for this case"; could duplicate the behaviour of the default
+                    // case instead, but this way we'd only need to change one place.
+                    goto default;
+                case JsonToken.TokenType.StringValue:
+                    return ParseSingleStringValue(field, token.StringValue);
+                // Note: not passing the number value itself here, as we may end up storing the string value in the token too.
+                case JsonToken.TokenType.Number:
+                    return ParseSingleNumberValue(field, token);
+                case JsonToken.TokenType.Null:
+                    throw new NotImplementedException("Haven't worked out what to do for null yet");
+                default:
+                    throw new InvalidProtocolBufferException("Unsupported JSON token type " + token.Type + " for field type " + fieldType);
+            }
+        }
+
+        /// <summary>
+        /// Parses <paramref name="json"/> into a new message.
+        /// </summary>
+        /// <typeparam name="T">The type of message to create.</typeparam>
+        /// <param name="json">The JSON to parse.</param>
+        public T Parse<T>(string json) where T : IMessage, new()
+        {
+            return Parse<T>(new StringReader(json));
+        }
+
+        /// <summary>
+        /// Parses JSON read from <paramref name="jsonReader"/> into a new message.
+        /// </summary>
+        /// <typeparam name="T">The type of message to create.</typeparam>
+        /// <param name="jsonReader">Reader providing the JSON to parse.</param>
+        public T Parse<T>(TextReader jsonReader) where T : IMessage, new()
+        {
+            T message = new T();
+            Merge(message, jsonReader);
+            return message;
+        }
+
+        private void MergeStructValue(IMessage message, JsonTokenizer tokenizer)
+        {
+            var firstToken = tokenizer.Next();
+            var fields = message.Descriptor.Fields;
+            switch (firstToken.Type)
+            {
+                case JsonToken.TokenType.Null:
+                    fields[Value.NullValueFieldNumber].Accessor.SetValue(message, 0);
+                    return;
+                case JsonToken.TokenType.StringValue:
+                    fields[Value.StringValueFieldNumber].Accessor.SetValue(message, firstToken.StringValue);
+                    return;
+                case JsonToken.TokenType.Number:
+                    fields[Value.NumberValueFieldNumber].Accessor.SetValue(message, firstToken.NumberValue);
+                    return;
+                case JsonToken.TokenType.False:
+                case JsonToken.TokenType.True:
+                    fields[Value.BoolValueFieldNumber].Accessor.SetValue(message, firstToken.Type == JsonToken.TokenType.True);
+                    return;
+                case JsonToken.TokenType.StartObject:
+                    {
+                        var field = fields[Value.StructValueFieldNumber];
+                        var structMessage = NewMessageForField(field);
+                        tokenizer.PushBack(firstToken);
+                        Merge(structMessage, tokenizer);
+                        field.Accessor.SetValue(message, structMessage);
+                        return;
+                    }
+                case JsonToken.TokenType.StartArray:
+                    {
+                        var field = fields[Value.ListValueFieldNumber];
+                        var list = NewMessageForField(field);
+                        tokenizer.PushBack(firstToken);
+                        Merge(list, tokenizer);
+                        field.Accessor.SetValue(message, list);
+                        return;
+                    }
+                default:
+                    throw new InvalidOperationException("Unexpected token type: " + firstToken.Type);
+            }
+        }
+
+        private void MergeStruct(IMessage message, JsonTokenizer tokenizer)
+        {
+            var token = tokenizer.Next();
+            if (token.Type != JsonToken.TokenType.StartObject)
+            {
+                throw new InvalidProtocolBufferException("Expected object value for Struct");
+            }
+            tokenizer.PushBack(token);
+
+            var field = message.Descriptor.Fields[Struct.FieldsFieldNumber];
+            MergeMapField(message, field, tokenizer);
+        }
+
+        #region Utility methods which don't depend on the state (or settings) of the parser.
+        private static object ParseMapKey(FieldDescriptor field, string keyText)
+        {
+            switch (field.FieldType)
+            {
+                case FieldType.Bool:
+                    if (keyText == "true")
+                    {
+                        return true;
+                    }
+                    if (keyText == "false")
+                    {
+                        return false;
+                    }
+                    throw new InvalidProtocolBufferException("Invalid string for bool map key: " + keyText);
+                case FieldType.String:
+                    return keyText;
+                case FieldType.Int32:
+                case FieldType.SInt32:
+                case FieldType.SFixed32:
+                    return ParseNumericString(keyText, int.Parse, false);
+                case FieldType.UInt32:
+                case FieldType.Fixed32:
+                    return ParseNumericString(keyText, uint.Parse, false);
+                case FieldType.Int64:
+                case FieldType.SInt64:
+                case FieldType.SFixed64:
+                    return ParseNumericString(keyText, long.Parse, false);
+                case FieldType.UInt64:
+                case FieldType.Fixed64:
+                    return ParseNumericString(keyText, ulong.Parse, false);
+                default:
+                    throw new InvalidProtocolBufferException("Invalid field type for map: " + field.FieldType);
+            }
+        }
+
+        private static object ParseSingleNumberValue(FieldDescriptor field, JsonToken token)
+        {
+            double value = token.NumberValue;
+            checked
+            {
+                // TODO: Validate that it's actually an integer, possibly in terms of the textual representation?                
+                try
+                {
+                    switch (field.FieldType)
+                    {
+                        case FieldType.Int32:
+                        case FieldType.SInt32:
+                        case FieldType.SFixed32:
+                            return (int) value;
+                        case FieldType.UInt32:
+                        case FieldType.Fixed32:
+                            return (uint) value;
+                        case FieldType.Int64:
+                        case FieldType.SInt64:
+                        case FieldType.SFixed64:
+                            return (long) value;
+                        case FieldType.UInt64:
+                        case FieldType.Fixed64:
+                            return (ulong) value;
+                        case FieldType.Double:
+                            return value;
+                        case FieldType.Float:
+                            if (double.IsNaN(value))
+                            {
+                                return float.NaN;
+                            }
+                            if (value > float.MaxValue || value < float.MinValue)
+                            {
+                                if (double.IsPositiveInfinity(value))
+                                {
+                                    return float.PositiveInfinity;
+                                }
+                                if (double.IsNegativeInfinity(value))
+                                {
+                                    return float.NegativeInfinity;
+                                }
+                                throw new InvalidProtocolBufferException("Value out of range: " + value);
+                            }
+                            return (float) value;
+                        default:
+                            throw new InvalidProtocolBufferException("Unsupported conversion from JSON number for field type " + field.FieldType);
+                    }
+                }
+                catch (OverflowException)
+                {
+                    throw new InvalidProtocolBufferException("Value out of range: " + value);
+                }
+            }
+        }
+
+        private static object ParseSingleStringValue(FieldDescriptor field, string text)
+        {
+            switch (field.FieldType)
+            {
+                case FieldType.String:
+                    return text;
+                case FieldType.Bytes:
+                    return ByteString.FromBase64(text);
+                case FieldType.Int32:
+                case FieldType.SInt32:
+                case FieldType.SFixed32:
+                    return ParseNumericString(text, int.Parse, false);
+                case FieldType.UInt32:
+                case FieldType.Fixed32:
+                    return ParseNumericString(text, uint.Parse, false);
+                case FieldType.Int64:
+                case FieldType.SInt64:
+                case FieldType.SFixed64:
+                    return ParseNumericString(text, long.Parse, false);
+                case FieldType.UInt64:
+                case FieldType.Fixed64:
+                    return ParseNumericString(text, ulong.Parse, false);
+                case FieldType.Double:
+                    double d = ParseNumericString(text, double.Parse, true);
+                    // double.Parse can return +/- infinity on Mono for non-infinite values which are out of range for double.
+                    if (double.IsInfinity(d) && !text.Contains("Infinity"))
+                    {
+                        throw new InvalidProtocolBufferException("Invalid numeric value: " + text);
+                    }
+                    return d;
+                case FieldType.Float:
+                    float f = ParseNumericString(text, float.Parse, true);
+                    // float.Parse can return +/- infinity on Mono for non-infinite values which are out of range for float.
+                    if (float.IsInfinity(f) && !text.Contains("Infinity"))
+                    {
+                        throw new InvalidProtocolBufferException("Invalid numeric value: " + text);
+                    }
+                    return f;
+                case FieldType.Enum:
+                    var enumValue = field.EnumType.FindValueByName(text);
+                    if (enumValue == null)
+                    {
+                        throw new InvalidProtocolBufferException("Invalid enum value: " + text + " for enum type: " + field.EnumType.FullName);
+                    }
+                    // Just return it as an int, and let the CLR convert it.
+                    return enumValue.Number;
+                default:
+                    throw new InvalidProtocolBufferException("Unsupported conversion from JSON string for field type " + field.FieldType);
+            }
+        }
+
+        /// <summary>
+        /// Creates a new instance of the message type for the given field.
+        /// This method is mostly extracted so we can replace it in one go when we work out
+        /// what we want to do instead of Activator.CreateInstance.
+        /// </summary>
+        private static IMessage NewMessageForField(FieldDescriptor field)
+        {
+            // TODO: Create an instance in a better way ?
+            // (We could potentially add a Parser property to MessageDescriptor... see issue 806.)
+            return (IMessage) Activator.CreateInstance(field.MessageType.GeneratedType);
+        }
+
+        private static T ParseNumericString<T>(string text, Func<string, NumberStyles, IFormatProvider, T> parser, bool floatingPoint)
+        {
+            // TODO: Prohibit leading zeroes (but allow 0!)
+            // TODO: Validate handling of "Infinity" etc. (Should be case sensitive, no leading whitespace etc)
+            // Can't prohibit this with NumberStyles.
+            if (text.StartsWith("+"))
+            {
+                throw new InvalidProtocolBufferException("Invalid numeric value: " + text);
+            }
+            if (text.StartsWith("0") && text.Length > 1)
+            {
+                if (text[1] >= '0' && text[1] <= '9')
+                {
+                    throw new InvalidProtocolBufferException("Invalid numeric value: " + text);
+                }
+            }
+            else if (text.StartsWith("-0") && text.Length > 2)
+            {
+                if (text[2] >= '0' && text[2] <= '9')
+                {
+                    throw new InvalidProtocolBufferException("Invalid numeric value: " + text);
+                }
+            }
+            try
+            {
+                var styles = floatingPoint
+                    ? NumberStyles.AllowLeadingSign | NumberStyles.AllowDecimalPoint | NumberStyles.AllowExponent
+                    : NumberStyles.AllowLeadingSign;
+                return parser(text, styles, CultureInfo.InvariantCulture);
+            }
+            catch (FormatException)
+            {
+                throw new InvalidProtocolBufferException("Invalid numeric value for type: " + text);
+            }
+            catch (OverflowException)
+            {
+                throw new InvalidProtocolBufferException("Value out of range: " + text);
+            }
+        }
+
+        private static void MergeTimestamp(IMessage message, JsonToken token)
+        {
+            if (token.Type != JsonToken.TokenType.StringValue)
+            {
+                throw new InvalidProtocolBufferException("Expected string value for Timestamp");
+            }
+            var match = TimestampRegex.Match(token.StringValue);
+            if (!match.Success)
+            {
+                throw new InvalidProtocolBufferException("Invalid Timestamp value: " + token.StringValue);
+            }
+            var dateTime = match.Groups["datetime"].Value;
+            var subseconds = match.Groups["subseconds"].Value;
+            var offset = match.Groups["offset"].Value;
+
+            try
+            {
+                DateTime parsed = DateTime.ParseExact(
+                    dateTime,
+                    "yyyy-MM-dd'T'HH:mm:ss",
+                    CultureInfo.InvariantCulture,
+                    DateTimeStyles.AssumeUniversal | DateTimeStyles.AdjustToUniversal);
+                // TODO: It would be nice not to have to create all these objects... easy to optimize later though.
+                Timestamp timestamp = Timestamp.FromDateTime(parsed);
+                int nanosToAdd = 0;
+                if (subseconds != "")
+                {
+                    // This should always work, as we've got 1-9 digits.
+                    int parsedFraction = int.Parse(subseconds.Substring(1), CultureInfo.InvariantCulture);
+                    nanosToAdd = parsedFraction * SubsecondScalingFactors[subseconds.Length];
+                }
+                int secondsToAdd = 0;
+                if (offset != "Z")
+                {
+                    // This is the amount we need to *subtract* from the local time to get to UTC - hence - => +1 and vice versa.
+                    int sign = offset[0] == '-' ? 1 : -1;
+                    int hours = int.Parse(offset.Substring(1, 2), CultureInfo.InvariantCulture);
+                    int minutes = int.Parse(offset.Substring(4, 2));
+                    int totalMinutes = hours * 60 + minutes;
+                    if (totalMinutes > 18 * 60)
+                    {
+                        throw new InvalidProtocolBufferException("Invalid Timestamp value: " + token.StringValue);
+                    }
+                    if (totalMinutes == 0 && sign == 1)
+                    {
+                        // This is an offset of -00:00, which means "unknown local offset". It makes no sense for a timestamp.
+                        throw new InvalidProtocolBufferException("Invalid Timestamp value: " + token.StringValue);
+                    }
+                    // We need to *subtract* the offset from local time to get UTC.
+                    secondsToAdd = sign * totalMinutes * 60;
+                }
+                // Ensure we've got the right signs. Currently unnecessary, but easy to do.
+                if (secondsToAdd < 0 && nanosToAdd > 0)
+                {
+                    secondsToAdd++;
+                    nanosToAdd = nanosToAdd - Duration.NanosecondsPerSecond;
+                }
+                if (secondsToAdd != 0 || nanosToAdd != 0)
+                {
+                    timestamp += new Duration { Nanos = nanosToAdd, Seconds = secondsToAdd };
+                    // The resulting timestamp after offset change would be out of our expected range. Currently the Timestamp message doesn't validate this
+                    // anywhere, but we shouldn't parse it.
+                    if (timestamp.Seconds < Timestamp.UnixSecondsAtBclMinValue || timestamp.Seconds > Timestamp.UnixSecondsAtBclMaxValue)
+                    {
+                        throw new InvalidProtocolBufferException("Invalid Timestamp value: " + token.StringValue);
+                    }
+                }
+                message.Descriptor.Fields[Timestamp.SecondsFieldNumber].Accessor.SetValue(message, timestamp.Seconds);
+                message.Descriptor.Fields[Timestamp.NanosFieldNumber].Accessor.SetValue(message, timestamp.Nanos);
+            }
+            catch (FormatException)
+            {
+                throw new InvalidProtocolBufferException("Invalid Timestamp value: " + token.StringValue);
+            }
+        }
+
+        private static void MergeDuration(IMessage message, JsonToken token)
+        {
+            if (token.Type != JsonToken.TokenType.StringValue)
+            {
+                throw new InvalidProtocolBufferException("Expected string value for Duration");
+            }
+            var match = DurationRegex.Match(token.StringValue);
+            if (!match.Success)
+            {
+                throw new InvalidProtocolBufferException("Invalid Duration value: " + token.StringValue);
+            }
+            var sign = match.Groups["sign"].Value;
+            var secondsText = match.Groups["int"].Value;
+            // Prohibit leading insignficant zeroes
+            if (secondsText[0] == '0' && secondsText.Length > 1)
+            {
+                throw new InvalidProtocolBufferException("Invalid Duration value: " + token.StringValue);
+            }
+            var subseconds = match.Groups["subseconds"].Value;
+            var multiplier = sign == "-" ? -1 : 1;
+
+            try
+            {
+                long seconds = long.Parse(secondsText, CultureInfo.InvariantCulture);
+                int nanos = 0;
+                if (subseconds != "")
+                {
+                    // This should always work, as we've got 1-9 digits.
+                    int parsedFraction = int.Parse(subseconds.Substring(1));
+                    nanos = parsedFraction * SubsecondScalingFactors[subseconds.Length];
+                }
+                if (seconds >= Duration.MaxSeconds)
+                {
+                    // Allow precisely 315576000000 seconds, but prohibit even 1ns more.
+                    if (seconds > Duration.MaxSeconds || nanos > 0)
+                    {
+                        throw new InvalidProtocolBufferException("Invalid Duration value: " + token.StringValue);
+                    }
+                }
+                message.Descriptor.Fields[Duration.SecondsFieldNumber].Accessor.SetValue(message, seconds * multiplier);
+                message.Descriptor.Fields[Duration.NanosFieldNumber].Accessor.SetValue(message, nanos * multiplier);
+            }
+            catch (FormatException)
+            {
+                throw new InvalidProtocolBufferException("Invalid Duration value: " + token.StringValue);
+            }
+        }
+
+        private static void MergeFieldMask(IMessage message, JsonToken token)
+        {
+            if (token.Type != JsonToken.TokenType.StringValue)
+            {
+                throw new InvalidProtocolBufferException("Expected string value for FieldMask");
+            }
+            // TODO: Do we *want* to remove empty entries? Probably okay to treat "" as "no paths", but "foo,,bar"?
+            string[] jsonPaths = token.StringValue.Split(FieldMaskPathSeparators, StringSplitOptions.RemoveEmptyEntries);
+            IList messagePaths = (IList) message.Descriptor.Fields[FieldMask.PathsFieldNumber].Accessor.GetValue(message);
+            foreach (var path in jsonPaths)
+            {
+                messagePaths.Add(ToSnakeCase(path));
+            }
+        }
+        
+        // Ported from src/google/protobuf/util/internal/utility.cc
+        private static string ToSnakeCase(string text)
+        {
+            var builder = new StringBuilder(text.Length * 2);
+            bool wasNotUnderscore = false;  // Initialize to false for case 1 (below)
+            bool wasNotCap = false;
+
+            for (int i = 0; i < text.Length; i++)
+            {
+                char c = text[i];
+                if (c >= 'A' && c <= 'Z') // ascii_isupper
+                {
+                    // Consider when the current character B is capitalized:
+                    // 1) At beginning of input:   "B..." => "b..."
+                    //    (e.g. "Biscuit" => "biscuit")
+                    // 2) Following a lowercase:   "...aB..." => "...a_b..."
+                    //    (e.g. "gBike" => "g_bike")
+                    // 3) At the end of input:     "...AB" => "...ab"
+                    //    (e.g. "GoogleLAB" => "google_lab")
+                    // 4) Followed by a lowercase: "...ABc..." => "...a_bc..."
+                    //    (e.g. "GBike" => "g_bike")
+                    if (wasNotUnderscore &&               //            case 1 out
+                        (wasNotCap ||                     // case 2 in, case 3 out
+                         (i + 1 < text.Length &&         //            case 3 out
+                          (text[i + 1] >= 'a' && text[i + 1] <= 'z')))) // ascii_islower(text[i + 1])
+                    {  // case 4 in
+                       // We add an underscore for case 2 and case 4.
+                        builder.Append('_');
+                    }
+                    // ascii_tolower, but we already know that c *is* an upper case ASCII character...
+                    builder.Append((char) (c + 'a' - 'A'));
+                    wasNotUnderscore = true;
+                    wasNotCap = false;
+                }
+                else
+                {
+                    builder.Append(c);
+                    wasNotUnderscore = c != '_';
+                    wasNotCap = true;
+                }
+            }
+            return builder.ToString();
+        }
+        #endregion
+
+        /// <summary>
+        /// Settings controlling JSON parsing. (Currently doesn't have any actual settings, but I suspect
+        /// we'll want them for levels of strictness, descriptor pools for Any handling, etc.)
+        /// </summary>
+        public sealed class Settings
+        {
+            private static readonly Settings defaultInstance = new Settings();
+
+            // TODO: Add recursion limit.
+
+            /// <summary>
+            /// Default settings, as used by <see cref="JsonParser.Default"/>
+            /// </summary>
+            public static Settings Default { get { return defaultInstance; } }
+
+            /// <summary>
+            /// Creates a new <see cref="Settings"/> object.
+            /// </summary>
+            public Settings()
+            {
+            }
+        }
+    }
+}
diff --git a/csharp/src/Google.Protobuf/JsonToken.cs b/csharp/src/Google.Protobuf/JsonToken.cs
new file mode 100644
index 0000000..6c0138c
--- /dev/null
+++ b/csharp/src/Google.Protobuf/JsonToken.cs
@@ -0,0 +1,166 @@
+﻿#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+using System;
+
+namespace Google.Protobuf
+{
+    internal sealed class JsonToken : IEquatable<JsonToken>
+    {
+        // Tokens with no value can be reused.
+        private static readonly JsonToken _true = new JsonToken(TokenType.True);
+        private static readonly JsonToken _false = new JsonToken(TokenType.False);
+        private static readonly JsonToken _null = new JsonToken(TokenType.Null);
+        private static readonly JsonToken startObject = new JsonToken(TokenType.StartObject);
+        private static readonly JsonToken endObject = new JsonToken(TokenType.EndObject);
+        private static readonly JsonToken startArray = new JsonToken(TokenType.StartArray);
+        private static readonly JsonToken endArray = new JsonToken(TokenType.EndArray);
+        private static readonly JsonToken endDocument = new JsonToken(TokenType.EndDocument);
+
+        internal static JsonToken Null { get { return _null; } }
+        internal static JsonToken False { get { return _false; } }
+        internal static JsonToken True { get { return _true; } }
+        internal static JsonToken StartObject{ get { return startObject; } }
+        internal static JsonToken EndObject { get { return endObject; } }
+        internal static JsonToken StartArray { get { return startArray; } }
+        internal static JsonToken EndArray { get { return endArray; } }
+        internal static JsonToken EndDocument { get { return endDocument; } }
+
+        internal static JsonToken Name(string name)
+        {
+            return new JsonToken(TokenType.Name, stringValue: name);
+        }
+
+        internal static JsonToken Value(string value)
+        {
+            return new JsonToken(TokenType.StringValue, stringValue: value);
+        }
+
+        internal static JsonToken Value(double value)
+        {
+            return new JsonToken(TokenType.Number, numberValue: value);
+        }
+
+        internal enum TokenType
+        {
+            Null,
+            False,
+            True,
+            StringValue,
+            Number,
+            Name,
+            StartObject,
+            EndObject,
+            StartArray,
+            EndArray,
+            EndDocument
+        }
+
+        // A value is a string, number, array, object, null, true or false
+        // Arrays and objects have start/end
+        // A document consists of a value
+        // Objects are name/value sequences.
+
+        private readonly TokenType type;
+        private readonly string stringValue;
+        private readonly double numberValue;
+
+        internal TokenType Type { get { return type; } }
+        internal string StringValue { get { return stringValue; } }
+        internal double NumberValue { get { return numberValue; } }
+
+        private JsonToken(TokenType type, string stringValue = null, double numberValue = 0)
+        {
+            this.type = type;
+            this.stringValue = stringValue;
+            this.numberValue = numberValue;
+        }
+
+        public override bool Equals(object obj)
+        {
+            return Equals(obj as JsonToken);
+        }
+
+        public override int GetHashCode()
+        {
+            unchecked
+            {
+                int hash = 17;
+                hash = hash * 31 + (int) type;
+                hash = hash * 31 + stringValue == null ? 0 : stringValue.GetHashCode();
+                hash = hash * 31 + numberValue.GetHashCode();
+                return hash;
+            }
+        }
+
+        public override string ToString()
+        {
+            switch (type)
+            {
+                case TokenType.Null:
+                    return "null";
+                case TokenType.True:
+                    return "true";
+                case TokenType.False:
+                    return "false";
+                case TokenType.Name:
+                    return "name (" + stringValue + ")";
+                case TokenType.StringValue:
+                    return "value (" + stringValue + ")";
+                case TokenType.Number:
+                    return "number (" + numberValue + ")";
+                case TokenType.StartObject:
+                    return "start-object";
+                case TokenType.EndObject:
+                    return "end-object";
+                case TokenType.StartArray:
+                    return "start-array";
+                case TokenType.EndArray:
+                    return "end-array";
+                case TokenType.EndDocument:
+                    return "end-document";
+                default:
+                    throw new InvalidOperationException("Token is of unknown type " + type);
+            }
+        }
+
+        public bool Equals(JsonToken other)
+        {
+            if (ReferenceEquals(other, null))
+            {
+                return false;
+            }
+            // Note use of other.numberValue.Equals rather than ==, so that NaN compares appropriately.
+            return other.type == type && other.stringValue == stringValue && other.numberValue.Equals(numberValue);
+        }
+    }
+}
diff --git a/csharp/src/Google.Protobuf/JsonTokenizer.cs b/csharp/src/Google.Protobuf/JsonTokenizer.cs
new file mode 100644
index 0000000..108cceb
--- /dev/null
+++ b/csharp/src/Google.Protobuf/JsonTokenizer.cs
@@ -0,0 +1,633 @@
+﻿#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+using System.Text;
+
+namespace Google.Protobuf
+{
+    /// <summary>
+    /// Simple but strict JSON tokenizer, rigidly following RFC 7159.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// This tokenizer is stateful, and only returns "useful" tokens - names, values etc.
+    /// It does not create tokens for the separator between names and values, or for the comma
+    /// between values. It validates the token stream as it goes - so callers can assume that the
+    /// tokens it produces are appropriate. For example, it would never produce "start object, end array."
+    /// </para>
+    /// <para>Not thread-safe.</para>
+    /// </remarks>
+    internal sealed class JsonTokenizer
+    {
+        // The set of states in which a value is valid next token.
+        private static readonly State ValueStates = State.ArrayStart | State.ArrayAfterComma | State.ObjectAfterColon | State.StartOfDocument;
+
+        private readonly Stack<ContainerType> containerStack = new Stack<ContainerType>();
+        private readonly PushBackReader reader;
+        private JsonToken bufferedToken;
+        private State state;
+
+        internal JsonTokenizer(TextReader reader)
+        {
+            this.reader = new PushBackReader(reader);
+            state = State.StartOfDocument;
+            containerStack.Push(ContainerType.Document);
+        }
+
+        internal void PushBack(JsonToken token)
+        {
+            if (bufferedToken != null)
+            {
+                throw new InvalidOperationException("Can't push back twice");
+            }
+            bufferedToken = token;
+        }
+
+        /// <summary>
+        /// Returns the next JSON token in the stream. An EndDocument token is returned to indicate the end of the stream,
+        /// after which point <c>Next()</c> should not be called again.
+        /// </summary>
+        /// <remarks>
+        /// This method essentially just loops through characters skipping whitespace, validating and
+        /// changing state (e.g. from ObjectBeforeColon to ObjectAfterColon)
+        /// until it reaches something which will be a genuine token (e.g. a start object, or a value) at which point
+        /// it returns the token. Although the method is large, it would be relatively hard to break down further... most
+        /// of it is the large switch statement, which sometimes returns and sometimes doesn't.
+        /// </remarks>
+        /// <returns>The next token in the stream. This is never null.</returns>
+        /// <exception cref="InvalidOperationException">This method is called after an EndDocument token has been returned</exception>
+        internal JsonToken Next()
+        {
+            if (bufferedToken != null)
+            {
+                var ret = bufferedToken;
+                bufferedToken = null;
+                return ret;
+            }
+            if (state == State.ReaderExhausted)
+            {
+                throw new InvalidOperationException("Next() called after end of document");
+            }
+            while (true)
+            {
+                var next = reader.Read();
+                if (next == null)
+                {
+                    ValidateState(State.ExpectedEndOfDocument, "Unexpected end of document in state: ");
+                    state = State.ReaderExhausted;
+                    return JsonToken.EndDocument;
+                }
+                switch (next.Value)
+                {
+                    // Skip whitespace between tokens
+                    case ' ':
+                    case '\t':
+                    case '\r':
+                    case '\n':
+                        break;
+                    case ':':
+                        ValidateState(State.ObjectBeforeColon, "Invalid state to read a colon: ");
+                        state = State.ObjectAfterColon;
+                        break;
+                    case ',':
+                        ValidateState(State.ObjectAfterProperty | State.ArrayAfterValue, "Invalid state to read a colon: ");
+                        state = state == State.ObjectAfterProperty ? State.ObjectAfterComma : State.ArrayAfterComma;
+                        break;
+                    case '"':
+                        string stringValue = ReadString();
+                        if ((state & (State.ObjectStart | State.ObjectAfterComma)) != 0)
+                        {
+                            state = State.ObjectBeforeColon;
+                            return JsonToken.Name(stringValue);
+                        }
+                        else
+                        {
+                            ValidateAndModifyStateForValue("Invalid state to read a double quote: ");
+                            return JsonToken.Value(stringValue);
+                        }
+                    case '{':
+                        ValidateState(ValueStates, "Invalid state to read an open brace: ");
+                        state = State.ObjectStart;
+                        containerStack.Push(ContainerType.Object);
+                        return JsonToken.StartObject;
+                    case '}':
+                        ValidateState(State.ObjectAfterProperty | State.ObjectStart, "Invalid state to read a close brace: ");
+                        PopContainer();
+                        return JsonToken.EndObject;
+                    case '[':
+                        ValidateState(ValueStates, "Invalid state to read an open square bracket: ");
+                        state = State.ArrayStart;
+                        containerStack.Push(ContainerType.Array);
+                        return JsonToken.StartArray;
+                    case ']':
+                        ValidateState(State.ArrayAfterValue | State.ArrayStart, "Invalid state to read a close square bracket: ");
+                        PopContainer();
+                        return JsonToken.EndArray;
+                    case 'n': // Start of null
+                        ConsumeLiteral("null");
+                        ValidateAndModifyStateForValue("Invalid state to read a null literal: ");
+                        return JsonToken.Null;
+                    case 't': // Start of true
+                        ConsumeLiteral("true");
+                        ValidateAndModifyStateForValue("Invalid state to read a true literal: ");
+                        return JsonToken.True;
+                    case 'f': // Start of false
+                        ConsumeLiteral("false");
+                        ValidateAndModifyStateForValue("Invalid state to read a false literal: ");
+                        return JsonToken.False;
+                    case '-': // Start of a number
+                    case '0':
+                    case '1':
+                    case '2':
+                    case '3':
+                    case '4':
+                    case '5':
+                    case '6':
+                    case '7':
+                    case '8':
+                    case '9':
+                        double number = ReadNumber(next.Value);
+                        ValidateAndModifyStateForValue("Invalid state to read a number token: ");
+                        return JsonToken.Value(number);
+                    default:
+                        throw new InvalidProtocolBufferException("Invalid first character of token: " + next.Value);
+                }
+            }
+        }
+
+        private void ValidateState(State validStates, string errorPrefix)
+        {
+            if ((validStates & state) == 0)
+            {
+                throw new InvalidProtocolBufferException(errorPrefix + state);
+            }
+        }
+
+        /// <summary>
+        /// Reads a string token. It is assumed that the opening " has already been read.
+        /// </summary>
+        private string ReadString()
+        {
+            var value = new StringBuilder();
+            bool haveHighSurrogate = false;
+            while (true)
+            {
+                char c = reader.ReadOrFail("Unexpected end of text while reading string");
+                if (c < ' ')
+                {
+                    throw new InvalidProtocolBufferException(string.Format(CultureInfo.InvariantCulture, "Invalid character in string literal: U+{0:x4}", (int) c));
+                }
+                if (c == '"')
+                {
+                    if (haveHighSurrogate)
+                    {
+                        throw new InvalidProtocolBufferException("Invalid use of surrogate pair code units");
+                    }
+                    return value.ToString();
+                }
+                if (c == '\\')
+                {
+                    c = ReadEscapedCharacter();
+                }
+                // TODO: Consider only allowing surrogate pairs that are either both escaped,
+                // or both not escaped. It would be a very odd text stream that contained a "lone" high surrogate
+                // followed by an escaped low surrogate or vice versa... and that couldn't even be represented in UTF-8.
+                if (haveHighSurrogate != char.IsLowSurrogate(c))
+                {
+                    throw new InvalidProtocolBufferException("Invalid use of surrogate pair code units");
+                }
+                haveHighSurrogate = char.IsHighSurrogate(c);
+                value.Append(c);
+            }
+        }
+
+        /// <summary>
+        /// Reads an escaped character. It is assumed that the leading backslash has already been read.
+        /// </summary>
+        private char ReadEscapedCharacter()
+        {
+            char c = reader.ReadOrFail("Unexpected end of text while reading character escape sequence");
+            switch (c)
+            {
+                case 'n':
+                    return '\n';
+                case '\\':
+                    return '\\';
+                case 'b':
+                    return '\b';
+                case 'f':
+                    return '\f';
+                case 'r':
+                    return '\r';
+                case 't':
+                    return '\t';
+                case '"':
+                    return '"';
+                case '/':
+                    return '/';
+                case 'u':
+                    return ReadUnicodeEscape();
+                default:
+                    throw new InvalidProtocolBufferException(string.Format(CultureInfo.InvariantCulture, "Invalid character in character escape sequence: U+{0:x4}", (int) c));
+            }
+        }
+
+        /// <summary>
+        /// Reads an escaped Unicode 4-nybble hex sequence. It is assumed that the leading \u has already been read.
+        /// </summary>
+        private char ReadUnicodeEscape()
+        {
+            int result = 0;
+            for (int i = 0; i < 4; i++)
+            {
+                char c = reader.ReadOrFail("Unexpected end of text while reading Unicode escape sequence");
+                int nybble;
+                if (c >= '0' && c <= '9')
+                {
+                    nybble = c - '0';
+                }
+                else if (c >= 'a' && c <= 'f')
+                {
+                    nybble = c - 'a' + 10;
+                }
+                else if (c >= 'A' && c <= 'F')
+                {
+                    nybble = c - 'A' + 10;
+                }
+                else
+                {
+                    throw new InvalidProtocolBufferException(string.Format(CultureInfo.InvariantCulture, "Invalid character in character escape sequence: U+{0:x4}", (int) c));
+                }
+                result = (result << 4) + nybble;
+            }
+            return (char) result;
+        }
+
+        /// <summary>
+        /// Consumes a text-only literal, throwing an exception if the read text doesn't match it.
+        /// It is assumed that the first letter of the literal has already been read.
+        /// </summary>
+        private void ConsumeLiteral(string text)
+        {
+            for (int i = 1; i < text.Length; i++)
+            {
+                char? next = reader.Read();
+                if (next == null)
+                {
+                    throw new InvalidProtocolBufferException("Unexpected end of text while reading literal token " + text);
+                }
+                if (next.Value != text[i])
+                {
+                    throw new InvalidProtocolBufferException("Unexpected character while reading literal token " + text);
+                }
+            }
+        }
+
+        private double ReadNumber(char initialCharacter)
+        {
+            StringBuilder builder = new StringBuilder();
+            if (initialCharacter == '-')
+            {
+                builder.Append("-");
+            }
+            else
+            {
+                reader.PushBack(initialCharacter);
+            }
+            // Each method returns the character it read that doesn't belong in that part,
+            // so we know what to do next, including pushing the character back at the end.
+            // null is returned for "end of text".
+            char? next = ReadInt(builder);
+            if (next == '.')
+            {
+                next = ReadFrac(builder);
+            }
+            if (next == 'e' || next == 'E')
+            {
+                next = ReadExp(builder);
+            }
+            // If we read a character which wasn't part of the number, push it back so we can read it again
+            // to parse the next token.
+            if (next != null)
+            {
+                reader.PushBack(next.Value);
+            }
+
+            // TODO: What exception should we throw if the value can't be represented as a double?
+            try
+            {
+                return double.Parse(builder.ToString(),
+                    NumberStyles.AllowLeadingSign | NumberStyles.AllowDecimalPoint | NumberStyles.AllowExponent,
+                    CultureInfo.InvariantCulture);
+            }
+            catch (OverflowException)
+            {
+                throw new InvalidProtocolBufferException("Numeric value out of range: " + builder);
+            }
+        }
+
+        private char? ReadInt(StringBuilder builder)
+        {
+            char first = reader.ReadOrFail("Invalid numeric literal");
+            if (first < '0' || first > '9')
+            {
+                throw new InvalidProtocolBufferException("Invalid numeric literal");
+            }
+            builder.Append(first);
+            int digitCount;
+            char? next = ConsumeDigits(builder, out digitCount);
+            if (first == '0' && digitCount != 0)
+            {
+                throw new InvalidProtocolBufferException("Invalid numeric literal: leading 0 for non-zero value.");
+            }
+            return next;
+        }
+
+        private char? ReadFrac(StringBuilder builder)
+        {
+            builder.Append('.'); // Already consumed this
+            int digitCount;
+            char? next = ConsumeDigits(builder, out digitCount);
+            if (digitCount == 0)
+            {
+                throw new InvalidProtocolBufferException("Invalid numeric literal: fraction with no trailing digits");
+            }
+            return next;
+        }
+
+        private char? ReadExp(StringBuilder builder)
+        {
+            builder.Append('E'); // Already consumed this (or 'e')
+            char? next = reader.Read();
+            if (next == null)
+            {
+                throw new InvalidProtocolBufferException("Invalid numeric literal: exponent with no trailing digits");
+            }
+            if (next == '-' || next == '+')
+            {
+                builder.Append(next.Value);
+            }
+            else
+            {
+                reader.PushBack(next.Value);
+            }
+            int digitCount;
+            next = ConsumeDigits(builder, out digitCount);
+            if (digitCount == 0)
+            {
+                throw new InvalidProtocolBufferException("Invalid numeric literal: exponent without value");
+            }
+            return next;
+        }
+
+        private char? ConsumeDigits(StringBuilder builder, out int count)
+        {
+            count = 0;
+            while (true)
+            {
+                char? next = reader.Read();
+                if (next == null || next.Value < '0' || next.Value > '9')
+                {
+                    return next;
+                }
+                count++;
+                builder.Append(next.Value);
+            }
+        }
+
+        /// <summary>
+        /// Validates that we're in a valid state to read a value (using the given error prefix if necessary)
+        /// and changes the state to the appropriate one, e.g. ObjectAfterColon to ObjectAfterProperty.
+        /// </summary>
+        private void ValidateAndModifyStateForValue(string errorPrefix)
+        {
+            ValidateState(ValueStates, errorPrefix);
+            switch (state)
+            {
+                case State.StartOfDocument:
+                    state = State.ExpectedEndOfDocument;
+                    return;
+                case State.ObjectAfterColon:
+                    state = State.ObjectAfterProperty;
+                    return;
+                case State.ArrayStart:
+                case State.ArrayAfterComma:
+                    state = State.ArrayAfterValue;
+                    return;
+                default:
+                    throw new InvalidOperationException("ValidateAndModifyStateForValue does not handle all value states (and should)");
+            }
+        }
+
+        /// <summary>
+        /// Pops the top-most container, and sets the state to the appropriate one for the end of a value
+        /// in the parent container.
+        /// </summary>
+        private void PopContainer()
+        {
+            containerStack.Pop();
+            var parent = containerStack.Peek();
+            switch (parent)
+            {
+                case ContainerType.Object:
+                    state = State.ObjectAfterProperty;
+                    break;
+                case ContainerType.Array:
+                    state = State.ArrayAfterValue;
+                    break;
+                case ContainerType.Document:
+                    state = State.ExpectedEndOfDocument;
+                    break;
+                default:
+                    throw new InvalidOperationException("Unexpected container type: " + parent);
+            }
+        }
+
+        private enum ContainerType
+        {
+            Document, Object, Array
+        }
+
+        /// <summary>
+        /// Possible states of the tokenizer.
+        /// </summary>
+        /// <remarks>
+        /// <para>This is a flags enum purely so we can simply and efficiently represent a set of valid states
+        /// for checking.</para>
+        /// <para>
+        /// Each is documented with an example,
+        /// where ^ represents the current position within the text stream. The examples all use string values,
+        /// but could be any value, including nested objects/arrays.
+        /// The complete state of the tokenizer also includes a stack to indicate the contexts (arrays/objects).
+        /// Any additional notional state of "AfterValue" indicates that a value has been completed, at which 
+        /// point there's an immediate transition to ExpectedEndOfDocument,  ObjectAfterProperty or ArrayAfterValue.
+        /// </para>
+        /// <para>
+        /// These states were derived manually by reading RFC 7159 carefully.
+        /// </para>
+        /// </remarks>
+        [Flags]
+        private enum State
+        {
+            /// <summary>
+            /// ^ { "foo": "bar" }
+            /// Before the value in a document. Next states: ObjectStart, ArrayStart, "AfterValue"
+            /// </summary>
+            StartOfDocument = 1 << 0,
+            /// <summary>
+            /// { "foo": "bar" } ^
+            /// After the value in a document. Next states: ReaderExhausted
+            /// </summary>
+            ExpectedEndOfDocument = 1 << 1,
+            /// <summary>
+            /// { "foo": "bar" } ^ (and already read to the end of the reader)
+            /// Terminal state.
+            /// </summary>
+            ReaderExhausted = 1 << 2,
+            /// <summary>
+            /// { ^ "foo": "bar" }
+            /// Before the *first* property in an object.
+            /// Next states:
+            /// "AfterValue" (empty object)
+            /// ObjectBeforeColon (read a name)
+            /// </summary>
+            ObjectStart = 1 << 3,
+            /// <summary>
+            /// { "foo" ^ : "bar", "x": "y" }
+            /// Next state: ObjectAfterColon
+            /// </summary>
+            ObjectBeforeColon = 1 << 4,
+            /// <summary>
+            /// { "foo" : ^ "bar", "x": "y" }
+            /// Before any property other than the first in an object.
+            /// (Equivalently: after any property in an object) 
+            /// Next states:
+            /// "AfterValue" (value is simple)
+            /// ObjectStart (value is object)
+            /// ArrayStart (value is array)
+            /// </summary>
+            ObjectAfterColon = 1 << 5,
+            /// <summary>
+            /// { "foo" : "bar" ^ , "x" : "y" }
+            /// At the end of a property, so expecting either a comma or end-of-object
+            /// Next states: ObjectAfterComma or "AfterValue"
+            /// </summary>
+            ObjectAfterProperty = 1 << 6,
+            /// <summary>
+            /// { "foo":"bar", ^ "x":"y" }
+            /// Read the comma after the previous property, so expecting another property.
+            /// This is like ObjectStart, but closing brace isn't valid here
+            /// Next state: ObjectBeforeColon.
+            /// </summary>
+            ObjectAfterComma = 1 << 7,
+            /// <summary>
+            /// [ ^ "foo", "bar" ]
+            /// Before the *first* value in an array.
+            /// Next states:
+            /// "AfterValue" (read a value)
+            /// "AfterValue" (end of array; will pop stack)
+            /// </summary>
+            ArrayStart = 1 << 8,
+            /// <summary>
+            /// [ "foo" ^ , "bar" ]
+            /// After any value in an array, so expecting either a comma or end-of-array
+            /// Next states: ArrayAfterComma or "AfterValue"
+            /// </summary>
+            ArrayAfterValue = 1 << 9,
+            /// <summary>
+            /// [ "foo", ^ "bar" ]
+            /// After a comma in an array, so there *must* be another value (simple or complex).
+            /// Next states: "AfterValue" (simple value), StartObject, StartArray
+            /// </summary>
+            ArrayAfterComma = 1 << 10
+        }
+
+        /// <summary>
+        /// Wrapper around a text reader allowing small amounts of buffering and location handling.
+        /// </summary>
+        private class PushBackReader
+        {
+            // TODO: Add locations for errors etc.
+
+            private readonly TextReader reader;
+
+            internal PushBackReader(TextReader reader)
+            {
+                // TODO: Wrap the reader in a BufferedReader?
+                this.reader = reader;
+            }
+
+            /// <summary>
+            /// The buffered next character, if we have one.
+            /// </summary>
+            private char? nextChar;
+
+            /// <summary>
+            /// Returns the next character in the stream, or null if we have reached the end.
+            /// </summary>
+            /// <returns></returns>
+            internal char? Read()
+            {
+                if (nextChar != null)
+                {
+                    char? tmp = nextChar;
+                    nextChar = null;
+                    return tmp;
+                }
+                int next = reader.Read();
+                return next == -1 ? null : (char?) next;
+            }
+
+            internal char ReadOrFail(string messageOnFailure)
+            {
+                char? next = Read();
+                if (next == null)
+                {
+                    throw new InvalidProtocolBufferException(messageOnFailure);
+                }
+                return next.Value;
+            }
+
+            internal void PushBack(char c)
+            {
+                if (nextChar != null)
+                {
+                    throw new InvalidOperationException("Cannot push back when already buffering a character");
+                }
+                nextChar = c;
+            }
+        }
+    }
+}
diff --git a/csharp/src/Google.Protobuf/MessageParser.cs b/csharp/src/Google.Protobuf/MessageParser.cs
index 6a6f101..70c52ba 100644
--- a/csharp/src/Google.Protobuf/MessageParser.cs
+++ b/csharp/src/Google.Protobuf/MessageParser.cs
@@ -142,5 +142,17 @@
             message.MergeFrom(input);
             return message;
         }
+
+        /// <summary>
+        /// Parses a message from the given JSON.
+        /// </summary>
+        /// <param name="json">The JSON to parse.</param>
+        /// <returns>The parsed message.</returns>
+        public T ParseJson(string json)
+        {
+            T message = factory();
+            JsonParser.Default.Merge(message, json);
+            return message;
+        }
     }
 }
diff --git a/csharp/src/Google.Protobuf/Properties/AssemblyInfo.cs b/csharp/src/Google.Protobuf/Properties/AssemblyInfo.cs
index 9a484ad..225ac0d 100644
--- a/csharp/src/Google.Protobuf/Properties/AssemblyInfo.cs
+++ b/csharp/src/Google.Protobuf/Properties/AssemblyInfo.cs
@@ -46,7 +46,10 @@
 [assembly: AssemblyCopyright("Copyright ©  2015")]
 [assembly: AssemblyTrademark("")]
 [assembly: AssemblyCulture("")]
+
+#if !NCRUNCH
 [assembly: AllowPartiallyTrustedCallers]
+#endif
 
 #if SIGNED
 [assembly: InternalsVisibleTo("Google.Protobuf.Test, PublicKey=" +
diff --git a/csharp/src/Google.Protobuf/WellKnownTypes/DurationPartial.cs b/csharp/src/Google.Protobuf/WellKnownTypes/DurationPartial.cs
index 18ebefd..324f48f 100644
--- a/csharp/src/Google.Protobuf/WellKnownTypes/DurationPartial.cs
+++ b/csharp/src/Google.Protobuf/WellKnownTypes/DurationPartial.cs
@@ -48,6 +48,16 @@
         public const int NanosecondsPerTick = 100;
 
         /// <summary>
+        /// The maximum permitted number of seconds.
+        /// </summary>
+        public const long MaxSeconds = 315576000000L;
+
+        /// <summary>
+        /// The minimum permitted number of seconds.
+        /// </summary>
+        public const long MinSeconds = -315576000000L;
+
+        /// <summary>
         /// Converts this <see cref="Duration"/> to a <see cref="TimeSpan"/>.
         /// </summary>
         /// <remarks>If the duration is not a precise number of ticks, it is truncated towards 0.</remarks>
diff --git a/csharp/src/Google.Protobuf/WellKnownTypes/TimestampPartial.cs b/csharp/src/Google.Protobuf/WellKnownTypes/TimestampPartial.cs
index 6858435..d284acd 100644
--- a/csharp/src/Google.Protobuf/WellKnownTypes/TimestampPartial.cs
+++ b/csharp/src/Google.Protobuf/WellKnownTypes/TimestampPartial.cs
@@ -38,6 +38,8 @@
     {
         private static readonly DateTime UnixEpoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
         private static readonly long BclSecondsAtUnixEpoch = UnixEpoch.Ticks / TimeSpan.TicksPerSecond;
+        internal static readonly long UnixSecondsAtBclMinValue = -BclSecondsAtUnixEpoch;
+        internal static readonly long UnixSecondsAtBclMaxValue = (DateTime.MaxValue.Ticks / TimeSpan.TicksPerSecond) - BclSecondsAtUnixEpoch;
 
         /// <summary>
         /// Returns the difference between one <see cref="Timestamp"/> and another, as a <see cref="Duration"/>.
diff --git a/csharp/src/Google.Protobuf/WellKnownTypes/ValuePartial.cs b/csharp/src/Google.Protobuf/WellKnownTypes/ValuePartial.cs
new file mode 100644
index 0000000..b4b6c05
--- /dev/null
+++ b/csharp/src/Google.Protobuf/WellKnownTypes/ValuePartial.cs
@@ -0,0 +1,99 @@
+﻿#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+namespace Google.Protobuf.WellKnownTypes
+{
+    public partial class Value
+    {
+        /// <summary>
+        /// Convenience method to create a Value message with a string value.
+        /// </summary>
+        /// <param name="value">Value to set for the StringValue property.</param>
+        /// <returns>A newly-created Value message with the given value.</returns>
+        public static Value ForString(string value)
+        {
+            Preconditions.CheckNotNull(value, "value");
+            return new Value { StringValue = value };
+        }
+
+        /// <summary>
+        /// Convenience method to create a Value message with a number value.
+        /// </summary>
+        /// <param name="value">Value to set for the NumberValue property.</param>
+        /// <returns>A newly-created Value message with the given value.</returns>
+        public static Value ForNumber(double value)
+        {
+            return new Value { NumberValue = value };
+        }
+
+        /// <summary>
+        /// Convenience method to create a Value message with a Boolean value.
+        /// </summary>
+        /// <param name="value">Value to set for the BoolValue property.</param>
+        /// <returns>A newly-created Value message with the given value.</returns>
+        public static Value ForBool(bool value)
+        {
+            return new Value { BoolValue = value };
+        }
+
+        /// <summary>
+        /// Convenience method to create a Value message with a null initial value.
+        /// </summary>
+        /// <returns>A newly-created Value message a null initial value.</returns>
+        public static Value ForNull()
+        {
+            return new Value { NullValue = 0 };
+        }
+
+        /// <summary>
+        /// Convenience method to create a Value message with an initial list of values.
+        /// </summary>
+        /// <remarks>The values provided are not cloned; the references are copied directly.</remarks>
+        /// <returns>A newly-created Value message an initial list value.</returns>
+        public static Value ForList(params Value[] values)
+        {
+            Preconditions.CheckNotNull(values, "values");
+            return new Value { ListValue = new ListValue { Values = { values } } };
+        }
+
+        /// <summary>
+        /// Convenience method to create a Value message with an initial struct value
+        /// </summary>
+        /// <remarks>The value provided is not cloned; the reference is copied directly.</remarks>
+        /// <returns>A newly-created Value message an initial struct value.</returns>
+        public static Value ForStruct(Struct value)
+        {
+            Preconditions.CheckNotNull(value, "value");
+            return new Value { StructValue = value };
+        }
+    }
+}
diff --git a/csharp/src/Google.Protobuf/WellKnownTypes/WrappersPartial.cs b/csharp/src/Google.Protobuf/WellKnownTypes/WrappersPartial.cs
new file mode 100644
index 0000000..efc13a0
--- /dev/null
+++ b/csharp/src/Google.Protobuf/WellKnownTypes/WrappersPartial.cs
@@ -0,0 +1,42 @@
+﻿#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2008 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+namespace Google.Protobuf.WellKnownTypes
+{
+    public static partial class Wrappers
+    {
+        /// <summary>
+        /// Field number for the single "value" field in all wrapper types.
+        /// </summary>
+        internal const int WrapperValueFieldNumber = Int32Value.ValueFieldNumber;
+    }
+}