This volume encompasses bilingualism from early childhood to adolescence, primarily in schools but also in other educational institutions. It addresses the special teaching and learning situations that affect more than 1 million multilingual students in German-speaking areas. The handbook provides a solid overview of the foundations, areas of action, and future developments in the field of German as a second language didactics. Against the backdrop of new research findings, it discusses conceptual foundations and competency areas of German for second language learners, as well as methodological questions, language proficiency diagnostics, and the conditions for second language acquisition both inside and outside the classroom. Furthermore, it outlines language didactic models that are relevant for the inclusive learning of children with and without a migration background in kindergartens and schools.