diff --git a/Doc/library/threading.rst b/Doc/library/threading.rst
index 371ac90..74c9976 100644
--- a/Doc/library/threading.rst
+++ b/Doc/library/threading.rst
@@ -17,11 +17,23 @@
    methods and functions in this module in the Python 2.x series are still
    supported by this module.
 
+.. impl-detail::
+
+   Due to the :term:`Global Interpreter Lock`, in CPython only one thread
+   can execute Python code at once (even though certain performance-oriented
+   libraries might overcome this limitation).
+   If you want your application to make better of use of the computational
+   resources of multi-core machines, you are advised to use
+   :mod:`multiprocessing` or :class:`concurrent.futures.ProcessPoolExecutor`.
+   However, threading is still an appropriate model if you want to run
+   multiple I/O-bound tasks simultaneously.
+
 .. seealso::
 
    Latest version of the :source:`threading module Python source code
    <Lib/threading.py>`
 
+
 This module defines the following functions and objects: