The nature of the debates surrounding international relations (IR) as a social science have pointed to issues of ontology, epistemology, methodology, philosophy of science, history, and sociology of knowledge, yet they are all crucial in understanding the character of international relations. Such an idea was brought about by Stanley Hoffman’s 1977 article, “An American Social Science: International Relations.” For Hoffmann, IR developed the way it did out of a set of distinctive intellectual predispositions, political circumstances, and institutional opportunities. His insights, however controversial, thus reveal fundamental questions about the work of IR scholars. The key issues here are the definition of IR as a discipline, the definition of IR as a science, and the definition of IR as an American social science in particular. The large variety of inquiries explored in IR, the “kind” of social science IR scholars are engaged in, as well as how “progress” is assessed, all reveal some important nuances in international relations as a discipline. Moreover, the debates surrounding the scientific legitimacy of IR scholarship reveal how IR gained legitimacy as a discipline. The historical development of IR could in fact be described as a series of debates, known among those in the field as the “great debates,” which eventually became the coherent whole understood to be the field of international relations.