diff --git a/CHANGES b/CHANGES
index 4e37d3b45..a136c7452 100644
--- a/CHANGES
+++ b/CHANGES
@@ -31,6 +31,7 @@ Bugs fixed
 * #3692: Unable to build HTML if writing .buildinfo failed
 * #4152: HTML writer crashes if a field list is placed on top of the document
 * #4063: Sphinx crashes when labeling directive ``.. todolist::``
+* #4134: [doc] :file:`docutils.conf` is not documented explicitly
 * #4169: Chinese language doesn't trigger Chinese search automatically
 
 Testing
diff --git a/doc/config.rst b/doc/config.rst
index a094195e9..e96c075e9 100644
--- a/doc/config.rst
+++ b/doc/config.rst
@@ -9,8 +9,20 @@ The build configuration file
    :synopsis: Build configuration file.
 
 The :term:`configuration directory` must contain a file named :file:`conf.py`.
-This file (containing Python code) is called the "build configuration file" and
-contains all configuration needed to customize Sphinx input and output behavior.
+This file (containing Python code) is called the "build configuration file"
+and contains (almost) all configuration needed to customize Sphinx input
+and output behavior.
+
+  An optional file `docutils.conf`_ can be added to the configuration
+  directory to adjust `Docutils`_ configuration if not otherwise overriden or
+  set by Sphinx; this applies in particular to the `Docutils smart_quotes
+  setting`_ (Note that Sphinx applies smart quotes transform by default.)
+
+  .. _`docutils`: http://docutils.sourceforge.net/
+
+  .. _`docutils.conf`: http://docutils.sourceforge.net/docs/user/config.html
+
+  .. _`Docutils smart_quotes setting`: http://docutils.sourceforge.net/docs/user/config.html#smart-quotes
 
 The configuration file is executed as Python code at build time (using
 :func:`execfile`, and with the current directory set to its containing
@@ -769,8 +781,8 @@ that use Sphinx's HTMLWriter class.
    entities.  Default: ``True``.
 
    .. deprecated:: 1.6
-      Use the `smart_quotes option`_ in the Docutils configuration file
-      (``docutils.conf``) instead.
+      To disable or customize smart quotes, use the Docutils configuration file
+      (``docutils.conf``) instead to set there its `smart_quotes option`_.
 
       .. _`smart_quotes option`: http://docutils.sourceforge.net/docs/user/config.html#smart-quotes