Why are multilateral institutions absent from some areas of international relations? Governments have not concluded regulatory policy agreements on tactical nuclear weapons and small arms control, deforestation, information privacy, and other transnational issues. The absence of regimes in such policy arenas is an empirical phenomenon with considerable theoretical and policy implications. Yet, existing scholarship on global governance largely ignores the instances in which such institutions do not emerge. This essay develops a research agenda to extend and strengthen regime theory through analysis of nonregimes. We articulate the concept, draw a typology of nonregimes, discuss the contributions that nonregime studies can make to IR theory, outline methodological approaches to pursue the proposed agenda, and highlight a priori theoretical considerations to guide such research. Six illustrative cases in the realms of arms control, environmental management, and international political economy are described and used to make preliminary observations of factors that impede regime formation.