The international relations (IR) discipline is dominated by the American research community. Data about publication patterns in leading journals document this situation as well as a variance in theoretical orientations. IR is conducted differently in different places. The main patterns are explained through a sociology of science model that emphasizes the different nineteenth-century histories of the state, the early format of social science, and the institutionalized delineation among the different social sciences. The internal social and intellectual structure of American IR is two-tiered, with relatively independent subfields and a top layer defined by access to the leading journals (on which IR, in contrast to some social sciences, has a high consensus). The famous successive “great debates” serve an important function by letting lead theorists focus and structure the whole discipline. IR in France, Germany, and the United Kingdom has historically been structured differently, often with power vested more locally. American IR now moves in a direction that undermines its global hegemony. The widespread turn to rational choice privileges a reintegration (and status-wise rehabilitation) with the rest of political science over attention to IR practices elsewhere. This rationalistic turn is alien to Europeans, both because their IR is generally closer to sociology, philosophy, and anthropology, and because the liberal ontological premises of rational choice are less fitting to European societies. Simultaneously, European IR is beginning to break the local power bastions and establish independent research communities at a national or, increasingly, a European level. As American IR turns from global hegemony to national professionalization, IR becomes more pluralistic.