The book is a current and comprehensive manual on German as a second language. It addresses all relevant aspects and provides scientifically grounded information on multilingualism in Germany and on teaching "German as a second language" in all its dimensions. It includes concepts for teaching German as a second language in both German and interdisciplinary instruction. The particular importance of language for the transmission of knowledge and its role in subject-specific learning, for example in the natural sciences, are among the central themes of the book. For effective teaching, it is essential to acquire structural knowledge of the first languages and to be aware of potential learning barriers as well as learner-friendly moments. Questions such as: Does the respective first language have articles, gender, and prepositions? How are the sentences structured? How does the verb organize the scene?.