International regimes are codes of conduct agreed upon by states to govern their relations in specific areas of international politics. This book describes and critically examines the three most important theories of international regimes. These theories each stress a particular explanatory variable: realist theories emphasize state power; neoliberal theories focus on constellations of interests; and cognitivist theories are concerned with knowledge and ideas. The authors conclude by exploring the prospects for progress within this dynamic field by combining different theoretical approaches.