diff --git a/Doc/library/functools.rst b/Doc/library/functools.rst
--- a/Doc/library/functools.rst
+++ b/Doc/library/functools.rst
@@ -445,6 +445,12 @@
    would have been ``'wrapper'``, and the docstring of the original :func:`example`
    would have been lost.
 
+.. function:: identity(obj)
+
+   Mathematical identity function which returns the argument unchanged.
+   If you have to ask when you would use this, you don't need to use this.
+
+   .. versionadded:: 3.6
 
 .. _partial-objects:
 
diff --git a/Lib/functools.py b/Lib/functools.py
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -85,6 +85,11 @@
                    assigned=assigned, updated=updated)
 
 
+def identity(obj):
+    """Mathematical identity function. Returns its argument unchanged."""
+    return obj
+
+
 ################################################################################
 ### total_ordering class decorator
 ################################################################################
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -1959,6 +1959,12 @@
         self.assertEqual(len(td), 0)
         functools.WeakKeyDictionary = _orig_wkd
 
+class TestIdentity(unittest.TestCase):
+    def test_identity(self):
+        identity = functools.identity
+        for obj in ["a b c", 99.99, [], {}, object(), (1,), [3, 4, 5]]:
+            self.assertIs(obj, identity(obj))
+
 
 if __name__ == '__main__':
     unittest.main()