This book provides an examination of the academic language found in Content and Language Integrated Learning (CLIL) primary-school written input, with a focus on the lexical demands of CLIL textbooks. CLIL is understood as the teaching of content subjects through an additional or foreign language. Under the CLIL approach, learners are asked to understand new concepts and ideas, while processing input that is unlikely to be comprehended without a broad L2 vocabulary knowledge. Within the total amount of L2 input they may receive, textbooks play a central role, as they are usually employed as guide for teachers and learners alike to vertebrate the curriculum. In this book the author focuses on the nature of the English textbooks to which CLIL learners are exposed and identifies the main lexical demands found in these texts. Following a corpus-based methodology, it analyses a corpus of 1.5 million words comprising CLIL primary-school textbooks from four disciplines: Arts & Crafts, Music, Natural Science and Social Science (Geography and History). This data-driven analysis explores the lexical demands posed by CLIL textbooks in each of these disciplines and offers a comparative exploration of these demands across subject areas and academic years. The volume will be of interest to researchers and practitioners interested in the linguistic implications of the application of a CLIL approach, including those with backgrounds in TESOL, Applied Linguistics, Curriculum and Materials Development, Second Language Acquisition and Language Education.