Why do governments form institutions devoted to emigrants and their descendants in the diaspora? Such institutions have become a regular feature of political life in many parts of the world: Over half all United Nations Member States now have one. Diaspora institutions merit research because they connect new developments in the global governance of migration with new patterns of national and transnational sovereignty and citizenship, and new ways of constructing individual identity in relation to new collectivities. But these institutions are generally overlooked. Migration policy is still understood as immigration policy, and research on diaspora institutions has been fragmented, case-study dominated, and largely descriptive. In this article, I review and extend the relevant theoretical literature and highlight empirical research priorities. I argue that existing studies focus too exclusively on national-level interests and ideas to explain how individual states tap diaspora resources and embrace these groups within the nation-state. However, these approaches cannot explain the global spread of diaspora institutions. This, I argue, requires a comparative approach and greater attention to the role of efforts to create a coherent but decentralized system of global governance in the area of international migration.