This contribution explores the „comparative turn“ in research on regionalism which emerged at the intersection of International Relations and area studies. Seeking to capture the rise of regionalism after the end of the Cold War, studies have increasingly engaged in comparisons of region-building in different parts of the world. Such inter-regional comparisons have revealed institutional similarities and convergence. We argue that theories of international cooperation and regional integration identify important drivers of regionalism in Europe and beyond; diffusion theories, however, are more adequate to account for institutional similarities and differences among regions. Nevertheless, we conclude with a plea not to pitch theories of diffusion, international cooperation and regional integration against each other but to view them as complementary approaches to comparative regionalism.