diff --git a/Doc/library/sys.rst b/Doc/library/sys.rst
--- a/Doc/library/sys.rst
+++ b/Doc/library/sys.rst
@@ -586,6 +586,34 @@
 
    Thus ``2.1.0a3`` is hexversion ``0x020100a3``.
 
+
+.. data:: implementation
+
+   An object containing the information about the implementation of the
+   currently running Python interpreter.  Its attributes are the those
+   that all Python implementations must implement.  They are described
+   below.
+
+   *name* is the implementation's identifer, like ``'cpython'``.
+
+   *version* is a named tuple, in the format of
+   :data:`sys.version_info`.  It represents the version of the Python
+   implementation, **not** the version of the Python language
+   specification it implements.
+
+   *hexversion* is the implementation version in hexadecimal format.
+
+   *cache_tag* is the tag used by the import machinery in the filenames
+   of cached modules, like ``'cpython-33'``.
+
+   Regardless of its contents, :data:`sys.implementation` will not
+   change during a run of the interpreter, nor between implementation
+   versions.  (It may change between Python language versions,
+   however.)  See `PEP 421` for more information.
+
+   .. versionadded:: 3.3
+
+
 .. data:: int_info
 
    A :term:`struct sequence` that holds information about Python's internal
diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
--- a/Lib/test/test_sys.py
+++ b/Lib/test/test_sys.py
@@ -577,6 +577,16 @@
             expected = None
         self.check_fsencoding(fs_encoding, expected)
 
+    def test_implementation(self):
+        # This test applies to all implementations equally.
+        self.assertTrue(hasattr(sys.implementation, 'name'))
+        self.assertTrue(hasattr(sys.implementation, 'version'))
+        self.assertTrue(hasattr(sys.implementation, 'hexversion'))
+        self.assertTrue(hasattr(sys.implementation, 'cache_tag'))
+
+        version = sys.implementation.version
+        self.assertEqual(version[:2], (version.major, version.minor))
+
 
 class SizeofTest(unittest.TestCase):