diff --git a/docs/x509/reference.rst b/docs/x509/reference.rst
index 9179468..65e3880 100644
--- a/docs/x509/reference.rst
+++ b/docs/x509/reference.rst
@@ -388,6 +388,89 @@
 
         The extensions encoded in the CRL.
 
+X.509 Certificate Builder
+~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. class:: CertificateBuilder
+
+    .. method:: __init__()
+
+        Creates an empty certificate (version 1).
+
+    .. method:: set_version(version)
+
+        Sets the X.509 version that will be used in the certificate.
+
+        :param version: The :class:`~cryptography.x509.Version` that will be
+            used by the certificate.
+
+    .. method:: set_issuer_name(name)
+
+        Sets the issuer's distinguished name.
+
+        :param public_key: The :class:`~cryptography.x509.Name` that describes
+            the issuer (CA).
+
+    .. method:: set_subject_name(name)
+
+        Sets the subject's distinguished name.
+
+        :param public_key: The :class:`~cryptography.x509.Name` that describes
+            the subject (requester).
+
+    .. method:: set_public_key(public_key)
+
+        Sets the subject's public key.
+
+        :param public_key: The subject's public key.
+
+    .. method:: set_serial_number(serial_number)
+
+        Sets the certificate's serial number (an integer).  The CA's policy
+        determines how it attributes serial numbers to certificates.  The only
+        requirement is that this number uniquely identify the certificate given
+        the issuer.
+
+        :param serial_number: Integer number that will be used by the CA to
+            identify this certificate (most notably during certificate
+            revocation checking).
+
+    .. method:: set_not_valid_before(time)
+
+        Sets the certificate's activation time.  This is the time from which
+        clients can start trusting the certificate.  It may be different from
+        the time at which the certificate was created.
+
+        :param time: The `datetime.datetime` object (in UTC) that marks the
+            activation time for the certificate.  The certificate may not be
+            trusted clients if it is used before this time.
+
+    .. method:: set_not_valid_after(time)
+
+        Sets the certificate's expiration time.  This is the time from which
+        clients should no longer trust the certificate.  The CA's policy will
+        determine how long the certificate should remain in use.
+
+        :param time: The `datetime.datetime` object (in UTC) that marks the
+            expiration time for the certificate.  The certificate may not be
+            trusted clients if it is used after this time.
+
+    .. method:: add_extension(extension)
+
+        Adds an X.509 extension to the certificate.
+
+        :param extension: The :class:`~cryptography.x509.Extension` to add to
+            the certificate.
+
+    .. method:: sign(backend, private_key, algorithm)
+
+        Sign the certificate using the CA's private key.
+
+        :param algorithm: The
+            :class:`~cryptography.hazmat.primitives.hashes.HashAlgorithm` that
+            will be used to generate the signature.
+
+
 X.509 CSR (Certificate Signing Request) Object
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
diff --git a/src/cryptography/hazmat/backends/openssl/backend.py b/src/cryptography/hazmat/backends/openssl/backend.py
index 7ccb39a..04f631f 100644
--- a/src/cryptography/hazmat/backends/openssl/backend.py
+++ b/src/cryptography/hazmat/backends/openssl/backend.py
@@ -4,6 +4,7 @@
 
 from __future__ import absolute_import, division, print_function
 
+import calendar
 import collections
 import itertools
 from contextlib import contextmanager
@@ -94,6 +95,22 @@
     return s
 
 
+def _make_asn1_int(backend, x):
+    i = backend._lib.ASN1_INTEGER_new()
+    # i = backend._ffi.gc(i, backend._lib.ASN1_INTEGER_free)
+    backend._lib.ASN1_INTEGER_set(i, x)
+    return i
+
+
+def _make_asn1_str(backend, x, n=None):
+    if n is None:
+        n = len(x)
+    s = backend._lib.ASN1_OCTET_STRING_new()
+    # s = backend._ffi.gc(s, backend._lib.ASN1_OCTET_STRING_free)
+    backend._lib.ASN1_OCTET_STRING_set(s, x, n)
+    return s
+
+
 def _encode_name(backend, attributes):
     """
     The X509_NAME created will not be gc'd. Use _encode_name_gc if needed.
@@ -988,6 +1005,85 @@
 
         return _CertificateSigningRequest(self, x509_req)
 
+    def sign_x509_certificate(self, builder, private_key, algorithm):
+        # TODO: check type of private key parameter.
+        if not isinstance(builder, x509.CertificateBuilder):
+            raise TypeError('Builder type mismatch.')
+        if not isinstance(algorithm, hashes.HashAlgorithm):
+            raise TypeError('Algorithm must be a registered hash algorithm.')
+
+        # Resolve the signature algorithm.
+        evp_md = self._lib.EVP_get_digestbyname(
+            algorithm.name.encode('ascii')
+        )
+        assert evp_md != self._ffi.NULL
+
+        # Create an empty certificate.
+        x509_cert = self._lib.X509_new()
+        x509_cert = self._ffi.gc(x509_cert, backend._lib.X509_free)
+
+        # Set the x509 version.
+        res = self._lib.X509_set_version(x509_cert, builder._version.value)
+        assert res == 1
+
+        # Set the subject's name.
+        res = self._lib.X509_set_subject_name(
+            x509_cert, _encode_name(self, list(builder._subject_name))
+        )
+        assert res == 1
+
+        # Set the subject's public key.
+        res = self._lib.X509_set_pubkey(
+            x509_cert, builder._public_key._evp_pkey
+        )
+        assert res == 1
+
+        # Set the certificate serial number.
+        serial_number = _make_asn1_int(self, builder._serial_number)
+        self._lib.X509_set_serialNumber(x509_cert, serial_number)
+
+        # Set the "not before" time.
+        res = self._lib.ASN1_TIME_set(
+            self._lib.X509_get_notBefore(x509_cert),
+            calendar.timegm(builder._not_valid_before.timetuple())
+        )
+        assert res != self._ffi.NULL
+
+        # Set the "not after" time.
+        res = self._lib.ASN1_TIME_set(
+            self._lib.X509_get_notAfter(x509_cert),
+            calendar.timegm(builder._not_valid_after.timetuple())
+        )
+        assert res != self._ffi.NULL
+
+        # Add extensions.
+        for i, extension in enumerate(builder._extensions):
+            if isinstance(extension.value, x509.BasicConstraints):
+                extension = _encode_basic_constraints(
+                    self,
+                    extension.value.ca,
+                    extension.value.path_length,
+                    extension.critical
+                )
+            else:
+                raise ValueError('Extension not yet supported.')
+            res = self._lib.X509_add_ext(x509_cert, extension, i)
+            assert res == 1
+
+        # Set the issuer name.
+        res = self._lib.X509_set_issuer_name(
+            x509_cert, _encode_name(self, list(builder._issuer_name))
+        )
+        assert res == 1
+
+        # Sign the certificate with the issuer's private key.
+        res = self._lib.X509_sign(
+            x509_cert, private_key._evp_pkey, evp_md
+        )
+        assert res > 0
+
+        return _Certificate(self, x509_cert)
+
     def load_pem_private_key(self, data, password):
         return self._load_key(
             self._lib.PEM_read_bio_PrivateKey,
diff --git a/src/cryptography/x509.py b/src/cryptography/x509.py
index 58e1a37..7cb42f5 100644
--- a/src/cryptography/x509.py
+++ b/src/cryptography/x509.py
@@ -5,6 +5,7 @@
 from __future__ import absolute_import, division, print_function
 
 import abc
+import datetime
 import ipaddress
 from email.utils import parseaddr
 from enum import Enum
@@ -1594,3 +1595,92 @@
         if self._subject_name is None:
             raise ValueError("A CertificateSigningRequest must have a subject")
         return backend.create_x509_csr(self, private_key, algorithm)
+
+
+class CertificateBuilder(object):
+    def __init__(self):
+        """
+        Creates an empty X.509 certificate (version 1).
+        """
+        self._version = Version.v1
+        self._issuer_name = None
+        self._subject_name = None
+        self._public_key = None
+        self._serial_number = None
+        self._not_valid_before = None
+        self._not_valid_after = None
+        self._extensions = []
+
+    def set_version(self, version):
+        """
+        Sets the X.509 version required by decoders.
+        """
+        if not isinstance(version, Version):
+            raise TypeError('Expecting x509.Version object.')
+        self._version = version
+
+    def set_issuer_name(self, name):
+        """
+        Sets the CA's distinguished name.
+        """
+        if not isinstance(name, Name):
+            raise TypeError('Expecting x509.Name object.')
+        self._issuer_name = name
+
+    def set_subject_name(self, name):
+        """
+        Sets the requestor's distinguished name.
+        """
+        if not isinstance(name, Name):
+            raise TypeError('Expecting x509.Name object.')
+        self._subject_name = name
+
+    def set_public_key(self, public_key):
+        """
+        Sets the requestor's public key (as found in the signing request).
+        """
+        # TODO: check type.
+        self._public_key = public_key
+
+    def set_serial_number(self, serial_number):
+        """
+        Sets the certificate serial number.
+        """
+        if not isinstance(serial_number, six.integer_types):
+            raise TypeError('Serial number must be of integral type.')
+        self._serial_number = serial_number
+
+    def set_not_valid_before(self, time):
+        """
+        Sets the certificate activation time.
+        """
+        # TODO: require UTC datetime?
+        if not isinstance(time, datetime.datetime):
+            raise TypeError('Expecting datetime object.')
+        self._not_valid_before = time
+
+    def set_not_valid_after(self, time):
+        """
+        Sets the certificate expiration time.
+        """
+        # TODO: require UTC datetime?
+        if not isinstance(time, datetime.datetime):
+            raise TypeError('Expecting datetime object.')
+        self._not_valid_after = time
+
+    def add_extension(self, extension):
+        """
+        Adds an X.509 extension to the certificate.
+        """
+        if not isinstance(extension, Extension):
+            raise TypeError('Expecting x509.Extension object.')
+        for e in self._extensions:
+            if e.oid == extension.oid:
+                raise ValueError('This extension has already been set.')
+        self._extensions.append(extension)
+
+    def sign(self, backend, private_key, algorithm):
+        """
+        Signs the certificate using the CA's private key.
+        """
+        return backend.sign_x509_certificate(self, private_key, algorithm)
diff --git a/tests/test_x509.py b/tests/test_x509.py
index 94eeab2..92f4047 100644
--- a/tests/test_x509.py
+++ b/tests/test_x509.py
@@ -775,6 +775,56 @@
         assert hash(request1) == hash(request2)
         assert hash(request1) != hash(request3)
 
+    def test_build_cert(self, backend):
+        issuer_private_key = rsa.generate_private_key(
+            public_exponent=65537,
+            key_size=2048,
+            backend=backend,
+        )
+        subject_private_key = rsa.generate_private_key(
+            public_exponent=65537,
+            key_size=2048,
+            backend=backend,
+        )
+
+        builder = x509.CertificateBuilder()
+        builder.set_version(x509.Version.v3)
+        builder.set_serial_number(777)
+        builder.set_issuer_name(x509.Name([
+            x509.NameAttribute(x509.OID_COUNTRY_NAME, 'US'),
+            x509.NameAttribute(x509.OID_STATE_OR_PROVINCE_NAME, 'Texas'),
+            x509.NameAttribute(x509.OID_LOCALITY_NAME, 'Austin'),
+            x509.NameAttribute(x509.OID_ORGANIZATION_NAME, 'PyCA'),
+            x509.NameAttribute(x509.OID_COMMON_NAME, 'cryptography.io'),
+        ]))
+        builder.set_subject_name(x509.Name([
+            x509.NameAttribute(x509.OID_COUNTRY_NAME, 'US'),
+            x509.NameAttribute(x509.OID_STATE_OR_PROVINCE_NAME, 'Texas'),
+            x509.NameAttribute(x509.OID_LOCALITY_NAME, 'Austin'),
+            x509.NameAttribute(x509.OID_ORGANIZATION_NAME, 'PyCA'),
+            x509.NameAttribute(x509.OID_COMMON_NAME, 'cryptography.io'),
+        ]))
+        builder.set_public_key(subject_private_key.public_key())
+        builder.add_extension(x509.Extension(
+            x509.OID_BASIC_CONSTRAINTS,
+            True,
+            x509.BasicConstraints(False, None),
+        ))
+        not_valid_before = datetime.datetime(2002, 1, 1, 12, 1)
+        not_valid_after = datetime.datetime(2030, 12, 31, 8, 30)
+        builder.set_not_valid_before(not_valid_before)
+        builder.set_not_valid_after(not_valid_after)
+        cert = builder.sign(backend, issuer_private_key, hashes.SHA1())
+
+        assert cert.version is x509.Version.v3
+        assert cert.not_valid_before == not_valid_before
+        assert cert.not_valid_after == not_valid_after
+        basic_constraints = cert.extensions.get_extension_for_oid(
+            x509.OID_BASIC_CONSTRAINTS
+        )
+        assert basic_constraints.value.ca is False
+        assert basic_constraints.value.path_length is None
+
 
 @pytest.mark.requires_backend_interface(interface=X509Backend)
 class TestCertificateSigningRequestBuilder(object):