The following paper discusses the chances of a middle-range theory for VET. Existing theories are either not well known or are based on a weak conceptual foundation. There is a mainly German tradition in defining, conceptualising and implementing VET as a theory. In the first part, we reconstruct this theoretically in the field of educational science-based approaches that emerged at the beginning of the 20th century. Since the late 1960s and 1970s, social science research flourished in this field, but marginalised the conceptual basis of Bildung and Beruf. This move was accompanied by an interdisciplinary expansion, but also by fatigue in the definition of central concepts of VET. This has also jeopardised the coherence of a VET research approach. However, we see an opportunity in the further development of a theory of VET that is not primarily rooted in one discipline, but still focuses on an educational perspective.