All international organizations exist in the conceptual and legal space between state sovereignty and legal obligation. They are built on a dilemma: they are created out of the commitments that sovereign states make to each other, and at the same time their reason for existing is to limit the choices of those same governments. They make use of the sovereign prerogatives of states in order to shape how those states use their sovereignty in the future. This chapter examines three forces in world politics: the commitments states make to international organizations, the choices states make regarding compliance and non-compliance with those commitments, and the powers of enforcement held by each international organization. Some international organizations are able to coerce their member states into complying with their commitments; for instance, the UN Security Council has a military component and the IMF has coercive leverage over its borrowers. But far more commonly international institutions are left to find more subtle ways to cajole or induce compliance from their members. In each organization, the specific balance between obligation, compliance, and enforcement is different and in turn this creates particular patterns of politics in the relations of each organization with its member-states. The main problems of international economics and international politics are at some level also problems of international organization, by which I mean that as interdependence between states increases, the importance of international organizations increases with it. International organizations are found, in one form or another, at the heart of all of the political and economic challenges of the twenty-first century. From international credit markets to endangered species to war crimes and torture, today's leading controversies all involve some measure of international commitment managed through formalized international organizations (IOs). Some IOs work well and some work hardly at all; some need reform, some need abolishing, and some need strengthening. To understand how this world works requires understanding the politics, powers, and limits of international organizations