CLIL has emerged since the millennium as a major trend in education. The book draws on the authors' experiences of CLIL in primary, secondary and English language schools across Europe. It summarizes the theory which underpins the teaching of a content subject through another language and discusses its practical application, outlining the key directions for the development of research and practice. The book acknowledges the uncertainty many teachers feel about CLIL, because of the requirement for both language and subject knowledge, while providing theoretical and practical routes towards successful practice for all. It is essential reading for both language and content-subject teachers.