The book develops the scientific and practical dimensions of didactics - understood as the theory of the relationship between teaching and learning - within a systematic theoretical framework that does not remain confined to the usual boundaries of school instruction but also includes teaching in pre-school, post-school, and extracurricular contexts. From the connection between education and instruction, the fundamental questions of general didactics are derived, with answers that are infinitely diverse. Against the backdrop of this breadth and complexity of didactics as a field of teaching and research, as well as a practical area of instruction, an overview of theoretical levels is provided, with exemplary discussions of practical and scientific theories. Readers, particularly students in educational professions, educational scientists, subject didacticians, and professional educators, are invited.