This book offers new empirical insights into the current state of Content and Language Integrated Learning (CLIL) characterisation (through an innovative proposal to link CLIL to English as a Lingua Franca), implementation (via observation protocols and SWOT analyses), and research (by examining the effects of CLIL on the L1, foreign language, key competences, and content subjects taught through English). The book provides a state of the art of the CLIL arena, identifies the chief challenges that need to be addressed and signposts possible ways of overcoming these in order to continue advancing smoothly into the next decade of CLIL development. This book will be of interest to researchers, policy-makers, educational authorities, and practitioners as it will assist them in making informed decisions about how to characterise, implement, and investigate CLIL in the bi- and plurilingual programs that are more frequently introduced in monolingual contexts.