International Relations (IR) scholars have long grappled with the production and diffusion of knowledge in their field. Using data on publications and scholars worldwide, this Element makes an empirical contribution to the 'Global IR' debate. We address two interrelated questions. First, how is the discipline structured in terms of (overlapping) research communities? We find evidence of a core-periphery system with great differences in visibility and interconnectedness. Following a hub-and-spoke pattern, peripheral communities have ties to the transatlantic core, but much less among themselves. Second, through which mechanisms does IR knowledge spread? Drawing on diffusion literature, we demonstrate that learning and emulation in citation practices foster the hub-and-spoke dynamic. Socialization also matters, as many scholars receive doctoral training in the transatlantic core. Competition helps explain heterogeneity and pluralism in IR. Overall, these diffusion mechanisms (re)produce the structuration of the discipline. This title is also available as Open Access on Cambridge Core.