This book explores the importance of language in content learning. It focuses on teachers' roles, knowledge and understanding of language in school contexts (including academic language and disciplinary languages) to support students. It examines teachers' language-related knowledge base for content teaching, which include teachers' knowledge of and about language, knowledge of (their) students and their pedagogical knowledge. This book also explores how teachers' knowledge of language, students and content are linked as part of a larger pedagogical content knowledge, which includes knowledge of the role of language in content learning. As well, it further considers literacy (and literacies) as part of this examination of teachers' knowledge of language.