Content and Language Integrated Learning (CLIL) refers to an educational context where a foreign language (in this case English) is used as a medium of instruction in content subjects. This book presents and analyses the changes which take place in a CLIL classroom in secondary education. This book will also serve to raise CLIL teachers' awareness of certain changes which occur in the CLIL classroom, and will consequently help them understand the process of Content and Language Integrated Learning. The book is organised into two parts: theoretical and empirical. These parts consist of six chapters each. The first three chapters review the professional literature relevant to this study, while the other three chapters are devoted to the empirical study.