diff --git a/README.md b/README.md
index a73e45ef..76a6ac1e 100644
--- a/README.md
+++ b/README.md
@@ -9,6 +9,10 @@ offers free country profiles in the public domain (that is, no copyright(s), no
 - [2] [Wikipedia Article: The World Factbook](http://en.wikipedia.org/wiki/The_World_Factbook)
 
 
+Note: All country profiles use the "official" two-letter GEC (formerly FIPS) codes and NOT the ISO codes (you
+might be used to) e.g. `au` for Austria (and not `at`), `gm` for Germany (and not `de`), and so on. 
+
+
 ## Examples
 
 Europe/Austria - `au.json`: