This chapter develops an analysis of where the OSCE stands in relationship to major schools of international relations theory, including liberal institutionalism, realism, and constructivism. It argues that the principles of the Helsinki Final Act sought to institutionalize liberal internationalist theory as the foundation for regional security cooperation. This entailed an application of democratic peace theory to the post-Cold War political regimes within the participating States and of theories of pluralistic security communities to the institutional framework for the OSCE region as a whole. It introduces the realist critique of this approach, which regained prominence in many parts of the OSCE region in the early twenty-first century, thereby undermining many of its foundational principles. It concludes by arguing from a constructivist perspective that the guiding principles of the OSCE are not determined by a static theory of international structures but rather reflect choices made by the governments of its participating States. In this respect, the OSCE is what its participating States “make of it.”