To be effective, an international regime must play a significant role in solving or at least managing the problem that led to its creation. But because regimes--social institutions composed of roles, rules, and relationships--are not actors in their own right, they can succeed only by influencing the behavior of their members or actors operating under their members' jurisdiction. This book examines how regimes influence the behavior of their members and those associated with them. It identifies six mechanisms through which regimes affect behavior and discusses the role of each through in-depth case studies of three major environmental concerns: intentional vessel-source oil pollution, shared fisheries, and transboundary acid rain. The behavioral mechanisms feature regimes as utility modifiers, as enhancers of cooperation, as bestowers of authority, as learning facilitators, as role definers, and as agents of internal realignments. The case studies show how these mechanisms can cause variations in effectiveness both across regimes and within individual regimes over time. One of the book's primary contributions is to develop methods to demonstrate which causal mechanisms come into play with specific regimes. It emphasizes the need to supplement conventional models assuming unitary and utility-maximizing actors to explain variations in regime effectiveness. Contributors include Lee G. Anderson, Ann Barrett, Marc A. Levy, Moira L. McConnell, Natalia Mirovitskaya, Ronald Mitchell, Don Munton, Elena Nikitina, Gail Osherenko, Alexei Roginko, Marvin Soroos, Olav Schram Stokke, Oran R. Young.