diff -r d9a3d23cf8f0 Doc/library/functions.rst
--- a/Doc/library/functions.rst	Tue Oct 14 00:53:13 2014 +0200
+++ b/Doc/library/functions.rst	Wed Oct 15 10:01:48 2014 +0100
@@ -1285,6 +1285,11 @@
    Use :func:`functools.cmp_to_key` to convert an old-style *cmp* function to a
    *key* function.
 
+   The built-in :func:`sorted` function is guaranteed to be stable. A sort is
+   stable if it guarantees not to change the relative order of elements that
+   compare equal --- this is helpful for sorting in multiple passes (for
+   example, sort by department, then by salary grade).
+
    For sorting examples and a brief sorting tutorial, see `Sorting HowTo
    <http://wiki.python.org/moin/HowTo/Sorting/>`_\.