diff --git a/libcxx/docs/Contributing.rst b/libcxx/docs/Contributing.rst
--- a/libcxx/docs/Contributing.rst
+++ b/libcxx/docs/Contributing.rst
@@ -25,6 +25,15 @@
 that your feature is already being worked on, please consider chiming in instead
 of duplicating work!
 
+RFCs for significant user-affecting changes
+===========================================
+
+Before you start working on a change that can have significant impact on users of the library,
+please consider creating a RFC on `libc++'s Discourse forum <https://discourse.llvm.org/c/runtimes/libcxx>`__.
+This will ensure that you work in a direction that the project endorses and will ease reviewing your
+contribution as directional questions can be raised early. Including a WIP patch is not mandatory, but
+it can be useful to ground the discussion in something concrete.
+
 Pre-commit check list
 =====================