The Common European Framework of Reference for Languages (CEF or CEFR) was produced by the Council of Europe in 2001, following extensive research and consultation. It describes learners’ language performance at six levels:

A1 and A2 : Basic user

B1 and B2: Independent User

C1 and C2: Proficient User.

It provides a common basis for learning, teaching and assessment across different languages, and the framework allows employers and educational institutions to compare qualifications. The descriptors also encourage self assessment, and have been integral to the development of the European Language Portfolio and the Languages ladder, as well as the National Language Standards which, like many ESOL qualifications, are aligned to the CEF.  See the Languages Ladder page for a table of equivalences.

You can download the CEF and find out much more at the Council of Europe website.