Language skills are essential prerequisites for a successful school career, as linguistic and content learning cannot be separated. Questions regarding language abilities and their promotion therefore pertain not only to German lessons but are relevant for all subjects. The engagement with language required in school demands from students abilities that go far beyond the linguistic management of everyday life. Furthermore, the cultural and language-related backgrounds of the students reflect the diversity of our society. Therefore, teachers need knowledge about language competencies and how they can be identified and promoted in the school environment. The practical volume addresses the societal and educational framework conditions as well as the educational and linguistic challenges of language competence in a multilingual context. Important findings from second language research and language didactics regarding the development and use of the central language skills of reading, writing, speaking, and listening, as well as their assessment, are presented. Additionally, the authors highlight development opportunities and support measures in secondary education. The study book focuses on a consistent connection between societal and linguistic scientific questions. It provides research-based foundational knowledge for teacher education students across all subjects, as well as for in-service secondary school teachers who wish to further their understanding of the connections between language competencies in first and second languages and educational success, and to learn practical methods for language support in adolescence.