diff --git a/.travis.yml b/.travis.yml
index 87673d7..ef51e7b 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -37,7 +37,7 @@
           env: TOXENV=py27 OPENSSL=1.1.0h
         - python: 3.5
           env: TOXENV=py35 OPENSSL=1.1.0h
-        - python: 2.7
+        - python: 3.6
           env: TOXENV=docs OPENSSL=1.1.0h
           addons:
               apt:
diff --git a/docs/fernet.rst b/docs/fernet.rst
index 2d7d228..9b95621 100644
--- a/docs/fernet.rst
+++ b/docs/fernet.rst
@@ -19,9 +19,9 @@
         >>> f = Fernet(key)
         >>> token = f.encrypt(b"my deep dark secret")
         >>> token
-        '...'
+        b'...'
         >>> f.decrypt(token)
-        'my deep dark secret'
+        b'my deep dark secret'
 
     :param bytes key: A URL-safe base64-encoded 32-byte key. This **must** be
                       kept secret. Anyone with this key is able to create and
@@ -113,9 +113,9 @@
         >>> f = MultiFernet([key1, key2])
         >>> token = f.encrypt(b"Secret message!")
         >>> token
-        '...'
+        b'...'
         >>> f.decrypt(token)
-        'Secret message!'
+        b'Secret message!'
 
     MultiFernet performs all encryption options using the *first* key in the
     ``list`` provided. MultiFernet attempts to decrypt tokens with each key in
@@ -152,14 +152,14 @@
            >>> f = MultiFernet([key1, key2])
            >>> token = f.encrypt(b"Secret message!")
            >>> token
-           '...'
+           b'...'
            >>> f.decrypt(token)
-           'Secret message!'
+           b'Secret message!'
            >>> key3 = Fernet(Fernet.generate_key())
            >>> f2 = MultiFernet([key3, key1, key2])
            >>> rotated = f2.rotate(token)
            >>> f2.decrypt(rotated)
-           'Secret message!'
+           b'Secret message!'
 
         :param bytes msg: The token to re-encrypt.
         :returns bytes: A secure message that cannot be read or altered without
@@ -205,9 +205,9 @@
     >>> f = Fernet(key)
     >>> token = f.encrypt(b"Secret message!")
     >>> token
-    '...'
+    b'...'
     >>> f.decrypt(token)
-    'Secret message!'
+    b'Secret message!'
 
 In this scheme, the salt has to be stored in a retrievable location in order
 to derive the same key from the password in the future.
diff --git a/docs/hazmat/primitives/aead.rst b/docs/hazmat/primitives/aead.rst
index 7b01f74..ee4214a 100644
--- a/docs/hazmat/primitives/aead.rst
+++ b/docs/hazmat/primitives/aead.rst
@@ -34,7 +34,7 @@
         >>> nonce = os.urandom(12)
         >>> ct = chacha.encrypt(nonce, data, aad)
         >>> chacha.decrypt(nonce, ct, aad)
-        'a secret message'
+        b'a secret message'
 
     .. classmethod:: generate_key()
 
@@ -99,7 +99,7 @@
         >>> nonce = os.urandom(12)
         >>> ct = aesgcm.encrypt(nonce, data, aad)
         >>> aesgcm.decrypt(nonce, ct, aad)
-        'a secret message'
+        b'a secret message'
 
     .. classmethod:: generate_key(bit_length)
 
@@ -181,7 +181,7 @@
         >>> nonce = os.urandom(13)
         >>> ct = aesccm.encrypt(nonce, data, aad)
         >>> aesccm.decrypt(nonce, ct, aad)
-        'a secret message'
+        b'a secret message'
 
     .. classmethod:: generate_key(bit_length)
 
diff --git a/docs/hazmat/primitives/asymmetric/ec.rst b/docs/hazmat/primitives/asymmetric/ec.rst
index edcfdfc..bbab224 100644
--- a/docs/hazmat/primitives/asymmetric/ec.rst
+++ b/docs/hazmat/primitives/asymmetric/ec.rst
@@ -669,7 +669,7 @@
     ...     encryption_algorithm=serialization.BestAvailableEncryption(b'testpassword')
     ... )
     >>> serialized_private.splitlines()[0]
-    '-----BEGIN ENCRYPTED PRIVATE KEY-----'
+    b'-----BEGIN ENCRYPTED PRIVATE KEY-----'
 
 You can also serialize the key without a password, by relying on
 :class:`~cryptography.hazmat.primitives.serialization.NoEncryption`.
@@ -685,7 +685,7 @@
     ...     format=serialization.PublicFormat.SubjectPublicKeyInfo
     ... )
     >>> serialized_public.splitlines()[0]
-    '-----BEGIN PUBLIC KEY-----'
+    b'-----BEGIN PUBLIC KEY-----'
 
 This is the part that you would normally share with the rest of the world.
 
diff --git a/docs/hazmat/primitives/asymmetric/rsa.rst b/docs/hazmat/primitives/asymmetric/rsa.rst
index 46cc30a..635a462 100644
--- a/docs/hazmat/primitives/asymmetric/rsa.rst
+++ b/docs/hazmat/primitives/asymmetric/rsa.rst
@@ -100,7 +100,7 @@
     ...    encryption_algorithm=serialization.BestAvailableEncryption(b'mypassword')
     ... )
     >>> pem.splitlines()[0]
-    '-----BEGIN ENCRYPTED PRIVATE KEY-----'
+    b'-----BEGIN ENCRYPTED PRIVATE KEY-----'
 
 It is also possible to serialize without encryption using
 :class:`~cryptography.hazmat.primitives.serialization.NoEncryption`.
@@ -113,7 +113,7 @@
     ...    encryption_algorithm=serialization.NoEncryption()
     ... )
     >>> pem.splitlines()[0]
-    '-----BEGIN RSA PRIVATE KEY-----'
+    b'-----BEGIN RSA PRIVATE KEY-----'
 
 For public keys you can use
 :meth:`~cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKey.public_bytes`
@@ -128,7 +128,7 @@
     ...    format=serialization.PublicFormat.SubjectPublicKeyInfo
     ... )
     >>> pem.splitlines()[0]
-    '-----BEGIN PUBLIC KEY-----'
+    b'-----BEGIN PUBLIC KEY-----'
 
 Signing
 ~~~~~~~
diff --git a/docs/hazmat/primitives/cryptographic-hashes.rst b/docs/hazmat/primitives/cryptographic-hashes.rst
index 7e23ce9..021e433 100644
--- a/docs/hazmat/primitives/cryptographic-hashes.rst
+++ b/docs/hazmat/primitives/cryptographic-hashes.rst
@@ -26,7 +26,7 @@
         >>> digest.update(b"abc")
         >>> digest.update(b"123")
         >>> digest.finalize()
-        'l\xa1=R\xcap\xc8\x83\xe0\xf0\xbb\x10\x1eBZ\x89\xe8bM\xe5\x1d\xb2\xd29%\x93\xafj\x84\x11\x80\x90'
+        b'l\xa1=R\xcap\xc8\x83\xe0\xf0\xbb\x10\x1eBZ\x89\xe8bM\xe5\x1d\xb2\xd29%\x93\xafj\x84\x11\x80\x90'
 
     If the backend doesn't support the requested ``algorithm`` an
     :class:`~cryptography.exceptions.UnsupportedAlgorithm` exception will be
diff --git a/docs/hazmat/primitives/mac/cmac.rst b/docs/hazmat/primitives/mac/cmac.rst
index b316e4c..a5b13ca 100644
--- a/docs/hazmat/primitives/mac/cmac.rst
+++ b/docs/hazmat/primitives/mac/cmac.rst
@@ -32,7 +32,7 @@
         >>> c = cmac.CMAC(algorithms.AES(key), backend=default_backend())
         >>> c.update(b"message to authenticate")
         >>> c.finalize()
-        'CT\x1d\xc8\x0e\x15\xbe4e\xdb\xb6\x84\xca\xd9Xk'
+        b'CT\x1d\xc8\x0e\x15\xbe4e\xdb\xb6\x84\xca\xd9Xk'
 
     If the backend doesn't support the requested ``algorithm`` an
     :class:`~cryptography.exceptions.UnsupportedAlgorithm` exception will be
diff --git a/docs/hazmat/primitives/mac/hmac.rst b/docs/hazmat/primitives/mac/hmac.rst
index a0e2014..c605e58 100644
--- a/docs/hazmat/primitives/mac/hmac.rst
+++ b/docs/hazmat/primitives/mac/hmac.rst
@@ -32,7 +32,7 @@
         >>> h = hmac.HMAC(key, hashes.SHA256(), backend=default_backend())
         >>> h.update(b"message to hash")
         >>> h.finalize()
-        '#F\xdaI\x8b"e\xc4\xf1\xbb\x9a\x8fc\xff\xf5\xdex.\xbc\xcd/+\x8a\x86\x1d\x84\'\xc3\xa6\x1d\xd8J'
+        b'#F\xdaI\x8b"e\xc4\xf1\xbb\x9a\x8fc\xff\xf5\xdex.\xbc\xcd/+\x8a\x86\x1d\x84\'\xc3\xa6\x1d\xd8J'
 
     If the backend doesn't support the requested ``algorithm`` an
     :class:`~cryptography.exceptions.UnsupportedAlgorithm` exception will be
diff --git a/docs/hazmat/primitives/padding.rst b/docs/hazmat/primitives/padding.rst
index e49fc49..245b554 100644
--- a/docs/hazmat/primitives/padding.rst
+++ b/docs/hazmat/primitives/padding.rst
@@ -25,16 +25,16 @@
         >>> padder = padding.PKCS7(128).padder()
         >>> padded_data = padder.update(b"11111111111111112222222222")
         >>> padded_data
-        '1111111111111111'
+        b'1111111111111111'
         >>> padded_data += padder.finalize()
         >>> padded_data
-        '11111111111111112222222222\x06\x06\x06\x06\x06\x06'
+        b'11111111111111112222222222\x06\x06\x06\x06\x06\x06'
         >>> unpadder = padding.PKCS7(128).unpadder()
         >>> data = unpadder.update(padded_data)
         >>> data
-        '1111111111111111'
+        b'1111111111111111'
         >>> data + unpadder.finalize()
-        '11111111111111112222222222'
+        b'11111111111111112222222222'
 
     :param block_size: The size of the block in :term:`bits` that the data is
         being padded to.
@@ -68,16 +68,16 @@
         >>> padder = padding.ANSIX923(128).padder()
         >>> padded_data = padder.update(b"11111111111111112222222222")
         >>> padded_data
-        '1111111111111111'
+        b'1111111111111111'
         >>> padded_data += padder.finalize()
         >>> padded_data
-        '11111111111111112222222222\x00\x00\x00\x00\x00\x06'
+        b'11111111111111112222222222\x00\x00\x00\x00\x00\x06'
         >>> unpadder = padding.ANSIX923(128).unpadder()
         >>> data = unpadder.update(padded_data)
         >>> data
-        '1111111111111111'
+        b'1111111111111111'
         >>> data + unpadder.finalize()
-        '11111111111111112222222222'
+        b'11111111111111112222222222'
 
     :param block_size: The size of the block in :term:`bits` that the data is
         being padded to.
diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst
index 126a918..593b880 100644
--- a/docs/hazmat/primitives/symmetric-encryption.rst
+++ b/docs/hazmat/primitives/symmetric-encryption.rst
@@ -42,7 +42,7 @@
         >>> ct = encryptor.update(b"a secret message") + encryptor.finalize()
         >>> decryptor = cipher.decryptor()
         >>> decryptor.update(ct) + decryptor.finalize()
-        'a secret message'
+        b'a secret message'
 
     :param algorithms: A
         :class:`~cryptography.hazmat.primitives.ciphers.CipherAlgorithm`
@@ -151,7 +151,7 @@
         >>> ct = encryptor.update(b"a secret message")
         >>> decryptor = cipher.decryptor()
         >>> decryptor.update(ct)
-        'a secret message'
+        b'a secret message'
 
 .. class:: TripleDES(key)
 
@@ -229,7 +229,7 @@
         >>> ct = encryptor.update(b"a secret message")
         >>> decryptor = cipher.decryptor()
         >>> decryptor.update(ct)
-        'a secret message'
+        b'a secret message'
 
 .. class:: IDEA(key)
 
@@ -278,7 +278,7 @@
     .. doctest::
 
         >>> from cryptography.hazmat.primitives.ciphers.modes import CBC
-        >>> iv = "a" * 16
+        >>> iv = b"a" * 16
         >>> mode = CBC(iv)
 
 
@@ -471,7 +471,7 @@
 
     .. testoutput::
 
-        a secret message!
+        b'a secret message!'
 
 .. class:: XTS(tweak)
 
@@ -594,7 +594,7 @@
             >>> len_decrypted = decryptor.update_into(ct, buf)
             >>> # get the plaintext from the buffer reading only the bytes written (len_decrypted)
             >>> bytes(buf[:len_decrypted]) + decryptor.finalize()
-            'a secret message'
+            b'a secret message'
 
     .. method:: finalize()
 
diff --git a/docs/spelling_wordlist.txt b/docs/spelling_wordlist.txt
index fb07fd0..160971d 100644
--- a/docs/spelling_wordlist.txt
+++ b/docs/spelling_wordlist.txt
@@ -96,6 +96,7 @@
 tunable
 Ubuntu
 unencrypted
+unicode
 unpadded
 unpadding
 verifier
diff --git a/docs/x509/reference.rst b/docs/x509/reference.rst
index 014d1f4..279c4c7 100644
--- a/docs/x509/reference.rst
+++ b/docs/x509/reference.rst
@@ -271,7 +271,7 @@
 
             >>> from cryptography.hazmat.primitives import hashes
             >>> cert.fingerprint(hashes.SHA256())
-            '\x86\xd2\x187Gc\xfc\xe7}[+E9\x8d\xb4\x8f\x10\xe5S\xda\x18u\xbe}a\x03\x08[\xac\xa04?'
+            b'\x86\xd2\x187Gc\xfc\xe7}[+E9\x8d\xb4\x8f\x10\xe5S\xda\x18u\xbe}a\x03\x08[\xac\xa04?'
 
     .. attribute:: serial_number
 
@@ -389,8 +389,8 @@
 
             >>> for ext in cert.extensions:
             ...     print(ext)
-            <Extension(oid=<ObjectIdentifier(oid=2.5.29.35, name=authorityKeyIdentifier)>, critical=False, value=<AuthorityKeyIdentifier(key_identifier='\xe4}_\xd1\\\x95\x86\x08,\x05\xae\xbeu\xb6e\xa7\xd9]\xa8f', authority_cert_issuer=None, authority_cert_serial_number=None)>)>
-            <Extension(oid=<ObjectIdentifier(oid=2.5.29.14, name=subjectKeyIdentifier)>, critical=False, value=<SubjectKeyIdentifier(digest='X\x01\x84$\x1b\xbc+R\x94J=\xa5\x10r\x14Q\xf5\xaf:\xc9')>)>
+            <Extension(oid=<ObjectIdentifier(oid=2.5.29.35, name=authorityKeyIdentifier)>, critical=False, value=<AuthorityKeyIdentifier(key_identifier=b'\xe4}_\xd1\\\x95\x86\x08,\x05\xae\xbeu\xb6e\xa7\xd9]\xa8f', authority_cert_issuer=None, authority_cert_serial_number=None)>)>
+            <Extension(oid=<ObjectIdentifier(oid=2.5.29.14, name=subjectKeyIdentifier)>, critical=False, value=<SubjectKeyIdentifier(digest=b'X\x01\x84$\x1b\xbc+R\x94J=\xa5\x10r\x14Q\xf5\xaf:\xc9')>)>
             <Extension(oid=<ObjectIdentifier(oid=2.5.29.15, name=keyUsage)>, critical=True, value=<KeyUsage(digital_signature=False, content_commitment=False, key_encipherment=False, data_encipherment=False, key_agreement=False, key_cert_sign=True, crl_sign=True, encipher_only=None, decipher_only=None)>)>
             <Extension(oid=<ObjectIdentifier(oid=2.5.29.32, name=certificatePolicies)>, critical=False, value=<CertificatePolicies([<PolicyInformation(policy_identifier=<ObjectIdentifier(oid=2.16.840.1.101.3.2.1.48.1, name=Unknown OID)>, policy_qualifiers=None)>])>)>
             <Extension(oid=<ObjectIdentifier(oid=2.5.29.19, name=basicConstraints)>, critical=True, value=<BasicConstraints(ca=True, path_length=None)>)>
@@ -461,7 +461,7 @@
 
             >>> from cryptography.hazmat.primitives import hashes
             >>> crl.fingerprint(hashes.SHA256())
-            'e\xcf.\xc4:\x83?1\xdc\xf3\xfc\x95\xd7\xb3\x87\xb3\x8e\xf8\xb93!\x87\x07\x9d\x1b\xb4!\xb9\xe4W\xf4\x1f'
+            b'e\xcf.\xc4:\x83?1\xdc\xf3\xfc\x95\xd7\xb3\x87\xb3\x8e\xf8\xb93!\x87\x07\x9d\x1b\xb4!\xb9\xe4W\xf4\x1f'
 
     .. attribute:: signature_hash_algorithm
 
@@ -501,7 +501,7 @@
         .. doctest::
 
             >>> crl.issuer
-            <Name([<NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.6, name=countryName)>, value=u'US')>, <NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.3, name=commonName)>, value=u'cryptography.io')>])>
+            <Name([<NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.6, name=countryName)>, value='US')>, <NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.3, name=commonName)>, value='cryptography.io')>])>
 
     .. attribute:: next_update
 
@@ -1132,9 +1132,9 @@
         3
         >>> for attribute in cert.subject:
         ...     print(attribute)
-        <NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.6, name=countryName)>, value=u'US')>
-        <NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.10, name=organizationName)>, value=u'Test Certificates 2011')>
-        <NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.3, name=commonName)>, value=u'Good CA')>
+        <NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.6, name=countryName)>, value='US')>
+        <NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.10, name=organizationName)>, value='Test Certificates 2011')>
+        <NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.3, name=commonName)>, value='Good CA')>
 
     .. attribute:: rdns
 
@@ -1152,7 +1152,7 @@
         .. doctest::
 
             >>> cert.subject.get_attributes_for_oid(NameOID.COMMON_NAME)
-            [<NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.3, name=commonName)>, value=u'Good CA')>]
+            [<NameAttribute(oid=<ObjectIdentifier(oid=2.5.4.3, name=commonName)>, value='Good CA')>]
 
     .. method:: public_bytes(backend)
 
@@ -1759,7 +1759,7 @@
             >>> from cryptography.hazmat.backends import default_backend
             >>> issuer_cert = x509.load_pem_x509_certificate(pem_data, default_backend())
             >>> x509.AuthorityKeyIdentifier.from_issuer_public_key(issuer_cert.public_key())
-            <AuthorityKeyIdentifier(key_identifier='X\x01\x84$\x1b\xbc+R\x94J=\xa5\x10r\x14Q\xf5\xaf:\xc9', authority_cert_issuer=None, authority_cert_serial_number=None)>
+            <AuthorityKeyIdentifier(key_identifier=b'X\x01\x84$\x1b\xbc+R\x94J=\xa5\x10r\x14Q\xf5\xaf:\xc9', authority_cert_issuer=None, authority_cert_serial_number=None)>
 
     .. classmethod:: from_issuer_subject_key_identifier(ski)
 
@@ -1790,7 +1790,7 @@
             >>> issuer_cert = x509.load_pem_x509_certificate(pem_data, default_backend())
             >>> ski = issuer_cert.extensions.get_extension_for_class(x509.SubjectKeyIdentifier)
             >>> x509.AuthorityKeyIdentifier.from_issuer_subject_key_identifier(ski)
-            <AuthorityKeyIdentifier(key_identifier='X\x01\x84$\x1b\xbc+R\x94J=\xa5\x10r\x14Q\xf5\xaf:\xc9', authority_cert_issuer=None, authority_cert_serial_number=None)>
+            <AuthorityKeyIdentifier(key_identifier=b'X\x01\x84$\x1b\xbc+R\x94J=\xa5\x10r\x14Q\xf5\xaf:\xc9', authority_cert_issuer=None, authority_cert_serial_number=None)>
 
 .. class:: SubjectKeyIdentifier(digest)
 
@@ -1837,7 +1837,7 @@
             >>> from cryptography.hazmat.backends import default_backend
             >>> csr = x509.load_pem_x509_csr(pem_req_data, default_backend())
             >>> x509.SubjectKeyIdentifier.from_public_key(csr.public_key())
-            <SubjectKeyIdentifier(digest='\xdb\xaa\xf0\x06\x11\xdbD\xfe\xbf\x93\x03\x8av\x88WP7\xa6\x91\xf7')>
+            <SubjectKeyIdentifier(digest=b'\xdb\xaa\xf0\x06\x11\xdbD\xfe\xbf\x93\x03\x8av\x88WP7\xa6\x91\xf7')>
 
 .. class:: SubjectAlternativeName(general_names)
 
@@ -1877,7 +1877,7 @@
             >>> ext = cert.extensions.get_extension_for_oid(ExtensionOID.SUBJECT_ALTERNATIVE_NAME)
             >>> # Get the dNSName entries from the SAN extension
             >>> ext.value.get_values_for_type(x509.DNSName)
-            [u'www.cryptography.io', u'cryptography.io']
+            ['www.cryptography.io', 'cryptography.io']
 
 
 .. class:: IssuerAlternativeName(general_names)
diff --git a/tox.ini b/tox.ini
index 6dfe1c7..a1e97c5 100644
--- a/tox.ini
+++ b/tox.ini
@@ -39,7 +39,7 @@
 extras =
     docs
     docstest
-basepython = python2.7
+basepython = python3
 commands =
     sphinx-build -j4 -T -W -b html -d {envtmpdir}/doctrees docs docs/_build/html
     sphinx-build -j4 -T -W -b latex -d {envtmpdir}/doctrees docs docs/_build/latex