Even though content and language integrated learning (CLIL) has been implemented in the Spanish educational system for some years now, it seems there is no consensus on whether this methodology is fulfilling its objectives. Although its practices in Spain have been studied in terms of assessment, language learning and content, research on students¿ and teachers¿ motivation in CLIL has been scarce. Taking into consideration that teaching and learning are social practices, it seems necessary to consider the affective factors such as motivation and perceptions which may come into play in CLIL practices. This book studies the perceptions and motivation regarding CLIL in three groups of CLIL physics and chemistry students and their CLIL teacher in a plurilingual high school located in Galicia.