diff --git a/maint/test/appengine/tox.ini b/maint/test/appengine/tox.ini
index 0970bf88..dcc7ac2f 100644
--- a/maint/test/appengine/tox.ini
+++ b/maint/test/appengine/tox.ini
@@ -5,14 +5,18 @@
 # These are currently excluded from the main tox.ini because their
 # logs are spammy and they're a little flaky.
 [tox]
-envlist = py25-appengine, py27-appengine
+envlist = py27-appengine
 
 [testenv]
 changedir = {toxworkdir}
 
+# py25-appengine was broken by the addition of unittest2.  Need to figure
+# out a way to smuggle unittest2 into the appengine environment if we don't
+# drop py25 support.
 [testenv:py25-appengine]
 basepython = python2.5
 commands = python {toxinidir}/py25/runtests.py {posargs:}
+deps = unittest2
 
 [testenv:py27-appengine]
 basepython = python2.7
diff --git a/tornado/test/escape_test.py b/tornado/test/escape_test.py
index defca1ba..793e3c8e 100644
--- a/tornado/test/escape_test.py
+++ b/tornado/test/escape_test.py
@@ -3,10 +3,10 @@
 
 from __future__ import absolute_import, division, with_statement
 import tornado.escape
-import unittest
 
 from tornado.escape import utf8, xhtml_escape, xhtml_unescape, url_escape, url_unescape, to_unicode, json_decode, json_encode
 from tornado.util import b
+from tornado.test.util import unittest
 
 linkify_tests = [
     # (input, linkify_kwargs, expected_output)
diff --git a/tornado/test/httpserver_test.py b/tornado/test/httpserver_test.py
index 190f1abc..41572715 100644
--- a/tornado/test/httpserver_test.py
+++ b/tornado/test/httpserver_test.py
@@ -10,6 +10,7 @@ from tornado.ioloop import IOLoop
 from tornado.iostream import IOStream
 from tornado.simple_httpclient import SimpleAsyncHTTPClient
 from tornado.testing import AsyncHTTPTestCase, AsyncHTTPSTestCase, AsyncTestCase, LogTrapTestCase
+from tornado.test.util import unittest
 from tornado.util import b, bytes_type
 from tornado.web import Application, RequestHandler
 import os
@@ -17,7 +18,6 @@ import shutil
 import socket
 import sys
 import tempfile
-import unittest
 
 try:
     import ssl
diff --git a/tornado/test/httputil_test.py b/tornado/test/httputil_test.py
index 736ed6d6..f1319cde 100644
--- a/tornado/test/httputil_test.py
+++ b/tornado/test/httputil_test.py
@@ -5,9 +5,9 @@ from __future__ import absolute_import, division, with_statement
 from tornado.httputil import url_concat, parse_multipart_form_data, HTTPHeaders
 from tornado.escape import utf8
 from tornado.testing import LogTrapTestCase
+from tornado.test.util import unittest
 from tornado.util import b
 import logging
-import unittest
 
 
 class TestUrlConcat(unittest.TestCase):
diff --git a/tornado/test/import_test.py b/tornado/test/import_test.py
index 584f070d..97c2277b 100644
--- a/tornado/test/import_test.py
+++ b/tornado/test/import_test.py
@@ -1,5 +1,5 @@
 from __future__ import absolute_import, division, with_statement
-import unittest
+from tornado.test.util import unittest
 
 
 class ImportTest(unittest.TestCase):
diff --git a/tornado/test/ioloop_test.py b/tornado/test/ioloop_test.py
index 2ebdbcea..4e5e123c 100644
--- a/tornado/test/ioloop_test.py
+++ b/tornado/test/ioloop_test.py
@@ -5,11 +5,11 @@ from __future__ import absolute_import, division, with_statement
 import datetime
 import socket
 import time
-import unittest
 
 from tornado.ioloop import IOLoop
 from tornado.netutil import bind_sockets
 from tornado.testing import AsyncTestCase, LogTrapTestCase, get_unused_port
+from tornado.test.util import unittest
 
 
 class TestIOLoop(AsyncTestCase, LogTrapTestCase):
diff --git a/tornado/test/locale_test.py b/tornado/test/locale_test.py
index 586080b1..4131dd0f 100644
--- a/tornado/test/locale_test.py
+++ b/tornado/test/locale_test.py
@@ -2,7 +2,7 @@ from __future__ import absolute_import, division, with_statement
 
 import os
 import tornado.locale
-import unittest
+from tornado.test.util import unittest
 
 
 class TranslationLoaderTest(unittest.TestCase):
diff --git a/tornado/test/options_test.py b/tornado/test/options_test.py
index 72be4459..c815935c 100644
--- a/tornado/test/options_test.py
+++ b/tornado/test/options_test.py
@@ -4,11 +4,11 @@ import logging
 import os
 import re
 import tempfile
-import unittest
 import warnings
 
 from tornado.escape import utf8
 from tornado.options import _Options, _LogFormatter
+from tornado.test.util import unittest
 from tornado.util import b, bytes_type
 
 
diff --git a/tornado/test/runtests.py b/tornado/test/runtests.py
index eea052ea..29c82d4d 100644
--- a/tornado/test/runtests.py
+++ b/tornado/test/runtests.py
@@ -2,7 +2,7 @@
 
 from __future__ import absolute_import, division, with_statement
 import sys
-import unittest
+from tornado.test.util import unittest
 
 TEST_MODULES = [
     'tornado.httputil.doctests',
diff --git a/tornado/test/stack_context_test.py b/tornado/test/stack_context_test.py
index dc717596..d911d169 100644
--- a/tornado/test/stack_context_test.py
+++ b/tornado/test/stack_context_test.py
@@ -3,12 +3,12 @@ from __future__ import absolute_import, division, with_statement
 
 from tornado.stack_context import StackContext, wrap
 from tornado.testing import AsyncHTTPTestCase, AsyncTestCase, LogTrapTestCase
+from tornado.test.util import unittest
 from tornado.util import b
 from tornado.web import asynchronous, Application, RequestHandler
 import contextlib
 import functools
 import logging
-import unittest
 
 
 class TestRequestHandler(RequestHandler):
diff --git a/tornado/test/testing_test.py b/tornado/test/testing_test.py
index 1de20df1..77f55e7e 100644
--- a/tornado/test/testing_test.py
+++ b/tornado/test/testing_test.py
@@ -1,9 +1,9 @@
 #!/usr/bin/env python
 
 from __future__ import absolute_import, division, with_statement
-import unittest
 import time
 from tornado.testing import AsyncTestCase, LogTrapTestCase
+from tornado.test.util import unittest
 
 
 class AsyncTestCaseTest(AsyncTestCase, LogTrapTestCase):
diff --git a/tornado/test/twisted_test.py b/tornado/test/twisted_test.py
index cd7fc60d..3178f94d 100644
--- a/tornado/test/twisted_test.py
+++ b/tornado/test/twisted_test.py
@@ -25,7 +25,6 @@ import signal
 import tempfile
 import thread
 import threading
-import unittest
 
 try:
     import fcntl
@@ -46,6 +45,7 @@ from tornado.httpclient import AsyncHTTPClient
 from tornado.ioloop import IOLoop
 from tornado.platform.auto import set_close_exec
 from tornado.testing import get_unused_port
+from tornado.test.util import unittest
 from tornado.util import import_object
 from tornado.web import RequestHandler, Application
 
diff --git a/tornado/test/util.py b/tornado/test/util.py
new file mode 100644
index 00000000..26d843d5
--- /dev/null
+++ b/tornado/test/util.py
@@ -0,0 +1,10 @@
+from __future__ import absolute_import, division, with_statement
+
+import sys
+
+# Encapsulate the choice of unittest or unittest2 here.
+# To be used as 'from tornado.test.util import unittest'.
+if sys.version_info >= (2, 7):
+    import unittest
+else:
+    import unittest2 as unittest
diff --git a/tornado/test/util_test.py b/tornado/test/util_test.py
index 8707b0d5..338c16a9 100644
--- a/tornado/test/util_test.py
+++ b/tornado/test/util_test.py
@@ -1,8 +1,8 @@
 from __future__ import absolute_import, division, with_statement
 import sys
-import unittest
 
 from tornado.util import raise_exc_info
+from tornado.test.util import unittest
 
 
 class RaiseExcInfoTest(unittest.TestCase):
@@ -23,4 +23,4 @@ class RaiseExcInfoTest(unittest.TestCase):
             raise_exc_info(exc_info)
             self.fail("didn't get expected exception")
         except TwoArgException, e:
-            self.assertTrue(e is exc_info[1])
+            self.assertIs(e, exc_info[1])
diff --git a/tornado/testing.py b/tornado/testing.py
index c18f17be..c597e3a7 100644
--- a/tornado/testing.py
+++ b/tornado/testing.py
@@ -41,7 +41,15 @@ import os
 import signal
 import sys
 import time
-import unittest
+
+# Tornado's own test suite requires the updated unittest module
+# (either py27+ or unittest2) so tornado.test.util enforces
+# this requirement, but for other users of tornado.testing we want
+# to allow the older version if unitest2 is not available.
+try:
+    import unittest2 as unittest
+except ImportError:
+    import unittest
 
 _next_port = 10000
 
diff --git a/tox.ini b/tox.ini
index e072d119..f4291e38 100644
--- a/tox.ini
+++ b/tox.ini
@@ -28,7 +28,9 @@ changedir = {toxworkdir}
 
 [testenv:py25]
 basepython = python2.5
-deps = simplejson
+deps =
+     simplejson
+     unittest2
 
 [testenv:py25-full]
 basepython = python2.5
@@ -38,9 +40,14 @@ deps =
      simplejson
      # twisted is dropping python 2.5 support in 12.2.0
      twisted<=12.1.0
+     unittest2
      # zope.interface (used by twisted) dropped python 2.5 support in 4.0
      zope.interface<4.0
 
+[testenv:py26]
+basepython = python2.6
+deps = unittest2
+
 # py26-full deliberately runs an older version of twisted to ensure
 # we're still compatible with the oldest version we support.
 [testenv:py26-full]
@@ -49,6 +56,7 @@ deps =
      MySQL-python
      pycurl
      twisted==11.0.0
+     unittest2
 
 [testenv:py27-full]
 basepython = python2.7