diff --git a/docs/language/core.rst b/docs/language/core.rst
index acdc025..9b24747 100644
--- a/docs/language/core.rst
+++ b/docs/language/core.rst
@@ -575,6 +575,26 @@ See also :ref:`remove-fn`.
    => (list (filter even? [1 2 3 -4 5 -7]))
    [2, -4]
 
+.. _flatten-fn:
+
+flatten
+-------
+
+.. versionadded:: 0.9.12
+
+Usage: ``(flatten coll)``
+
+Return a single list of all the items in ``coll``, by flattening all
+contained lists and/or tuples.
+
+.. code-block:: clojure
+
+   => (flatten [1 2 [3 4] 5])
+   [1, 2, 3, 4, 5]
+
+   => (flatten ["foo" (, 1 2) [1 [2 3] 4] "bar"])
+   ['foo', 1, 2, 1, 2, 3, 4, 'bar']
+
 
 .. _iterate-fn: