Empirical research on teachers' professional knowledge is mostly conducted worldwide with reference to the construct 'pedagogical content knowledge' (PCK) introduced by Lee S. Shulman. In the 'Consensus Model' (CM) and the 'Refined Consensus Model' (RCM), PCK was further developed and differentiated. Nevertheless, neither PCK nor CM and RCM adequately capture the complexity of teachers' professional knowledge. Thus, educational-theoretical foundations and goals of subject-specific teaching and learning are not sufficiently taken into account. The same applies to personal, emotional and reflective goals of subject-matter education. Against this background, we propose a more comprehensive model, which we call "subject-specific didactic knowledge" (SDK) and which is based on the distinction between two complementary basic forms of subject-specific education (SME): a functional form of SME in the tradition of PCK and literacy (OECD / PISA) and a personal form of SME, which is characterized by the German educational tradition (sensu Wilhelm von Humboldt) and the US-American philosophy of education (sensu George Herbert Mead and John Dewey). We illustrate the practical implications of this approach for subject-matter education and its investigation, using examples from empirical research in curricular based models of teaching and learning in Germany and other countries.