Content and language integrated learning (CLIL) has become a well-known term for foreign language teachers and language researchers. A little more than a decade ago, it was a term unheard of in most staff rooms or professional conferences. This paper seeks to define CLIL and to look into the reasons that have propelled it to widespread adoption. Important success factors of CLIL programmes will be presented, as well as research results relating to its impact. Finally, concerns about CLIL will be addressed and a way forward for the approach will be roughly sketched.