In assessing population as an intergovernmental and world issue, historians have generally focused on the politics of sex, gender, and reproduction. To expect the history of population to be solely or even primarily about reproduction and individual health, however, is to miss entirely other lines of thought within which population, and in particular world population, came to be a problem for international organizations of the twentieth century. The problematization of population often raised questions about and plans for migration, colonial expansion of territory, and the properties of land and soil—in other words, geopolitics. This article shows how the population problem was precisely a geopolitical problem for the late League of Nations and the early United Nations. The article discusses two institutional occasions on which population as a spatial and security problem came onto the agenda of international organizations. The fi rst case involved a series of meetings held by the International Institute of Intellectual Co-operation, resulting in the document Peaceful Change (1937). The second case arose in the early years of UNESCO when Julian Huxley and others attempted to raise population as a major world issue.