diff --git a/wp-includes/theme.php b/wp-includes/theme.php
index 877e7c7658..c58a9f51c9 100644
--- a/wp-includes/theme.php
+++ b/wp-includes/theme.php
@@ -6,6 +6,17 @@
  * @subpackage Template
  */
 
+/**
+ * Whether a child theme is in use.
+ *
+ * @since 3.0.0
+ *
+ * @return bool true if a child theme is in use, false otherwise.
+ **/
+function is_child_theme() {
+	return ( TEMPLATEPATH !== STYLESHEETPATH );
+}
+
 /**
  * Retrieve name of the current stylesheet.
  *