diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst
index eafd70a..08938b2 100644
--- a/Doc/reference/expressions.rst
+++ b/Doc/reference/expressions.rst
@@ -1315,8 +1315,9 @@ Identity comparisons
 --------------------
 
 The operators :keyword:`is` and :keyword:`is not` test for object identity: ``x
-is y`` is true if and only if *x* and *y* are the same object.  ``x is not y``
-yields the inverse truth value. [#]_
+is y`` is true if and only if *x* and *y* are the same object.  Object identity
+is determined using the :meth:`id` function.  ``x is not y`` yields the inverse
+truth value. [#]_
 
 
 .. _booleans: