Theories of international regimes, as discussed by Haggard and Simmons, have become a major focus in international relations research over the past decade. The interest in regimes stems from dissatisfaction with traditional views of international order, authority, and organization. The contrast between the competitive, zero-sum nature of interstate relations and the authority of domestic politics has led to a reevaluation of cooperative behavior among advanced industrial states. The growth of interdependence since World War II has created new forms of coordination and organization that do not fit neatly into a realist framework. Realism has traditionally questioned the importance of international law and its study by political scientists. However, the study of international organizations and regional integration has generated rich theoretical debates. Regime analysis aims to bridge the gap between idealist and realist traditions by focusing on norms and their influence on state behavior, while acknowledging the pursuit of national interests. Regime analysis has developed over the past decade, with various theories explaining regime creation, maintenance, and transformation. However, the relationship among these theories is unclear, and empirical research has yet to determine which are more plausible. Recent work on regimes and international cooperation has reverted to an approach that treats states as unified, rational actors, neglecting the role of non-state actors and international organizations. The authors survey different definitions of international regimes, ranging from patterned behavior to explicit injunctions. They suggest dimensions along which regimes vary, such as strength, organizational form, scope, and allocational mode. The third section examines four theoretical approaches to regimes—structural, game-theoretic, functional, and cognitive—and attempts to clarify what each theory can and cannot tell us about regimes. The conclusion asks how and whether regimes "matter." The authors argue that regimes have independent influence on state behavior, but this is not yet well understood. They suggest a research program that focuses on issues raised by theorists of complex interdependence, including the boundaries between domestic and foreign policies, the importance of transnational coalitions, and the role of domestic political forces in international cooperation. The authors also highlight the need to consider domestic political processes in understanding international regimes, as well as the importance of consensus and knowledge in explaining cooperation.Theories of international regimes, as discussed by Haggard and Simmons, have become a major focus in international relations research over the past decade. The interest in regimes stems from dissatisfaction with traditional views of international order, authority, and organization. The contrast between the competitive, zero-sum nature of interstate relations and the authority of domestic politics has led to a reevaluation of cooperative behavior among advanced industrial states. The growth of interdependence since World War II has created new forms of coordination and organization that do not fit neatly into a realist framework. Realism has traditionally questioned the importance of international law and its study by political scientists. However, the study of international organizations and regional integration has generated rich theoretical debates. Regime analysis aims to bridge the gap between idealist and realist traditions by focusing on norms and their influence on state behavior, while acknowledging the pursuit of national interests. Regime analysis has developed over the past decade, with various theories explaining regime creation, maintenance, and transformation. However, the relationship among these theories is unclear, and empirical research has yet to determine which are more plausible. Recent work on regimes and international cooperation has reverted to an approach that treats states as unified, rational actors, neglecting the role of non-state actors and international organizations. The authors survey different definitions of international regimes, ranging from patterned behavior to explicit injunctions. They suggest dimensions along which regimes vary, such as strength, organizational form, scope, and allocational mode. The third section examines four theoretical approaches to regimes—structural, game-theoretic, functional, and cognitive—and attempts to clarify what each theory can and cannot tell us about regimes. The conclusion asks how and whether regimes "matter." The authors argue that regimes have independent influence on state behavior, but this is not yet well understood. They suggest a research program that focuses on issues raised by theorists of complex interdependence, including the boundaries between domestic and foreign policies, the importance of transnational coalitions, and the role of domestic political forces in international cooperation. The authors also highlight the need to consider domestic political processes in understanding international regimes, as well as the importance of consensus and knowledge in explaining cooperation.