In this article, we explore the concept of 'powerful knowledge' which, from a curriculum studies perspective, refers to the aspects of content knowledge towards which teaching should be oriented. We then consider how the concept of 'powerful knowledge' can be developed and operationalized as a research framework within studies in subject-specific didactics across the curriculum by relating it to the analytical concept of 'transformation'. Transformation is perceived in this case as an integrative process in which content knowledge is transformed into knowledge that is taught and learned through various transformation processes both outside and within the educational system. We argue that powerful knowledge cannot be identified based on the discipline alone, but needs to consider transformation processes and be empirically explored. A variety of theories and frameworks developed within the European research tradition of didactics are described as ways to study transformation processes related to powerful knowledge at different institutional levels as well as between different subjects and disciplines. A comparative research framework related to subject-specific education is proposed around three research questions.