This chapter lays out the theoretical foundations of the argument the book proposes to explain differences in the coevolution of health care and public health. In short, I con- tend that that professionalism and interest intermediation, unified government, as well as contextual elements, such as technological novelties or economic development, need to be taken into account to understand the coevolution of health care and public health. The chapter has two parts: firstly, I elaborate on the argument in general terms; secondly, I discuss the implications for health care and public health. In each part, I start with a discussion of the broad institutionalist approach and turn then to the literature on the politicization of professions and interest group inclusion, unified government and contex- tual conditions. I am harkening back to the research on the politicization of professions and interest group inclusion to develop a hypothesis on the responsiveness between policy sectors. To hypothesize on the institutional relations of policy sectors, I am employing the notion of unified government (veto players and federalism).