Systems of policy coordination since 1945 may be classified as rule-governed systems relying on decentralized national decisions (a stylized Bretton Woods system) or discretionary bargaining in which coordination decisions are taken collectively at the international level (e.g. world economic summits). The European Monetary System combines elements of these two models. National attachments to rules cannot be explained solely by the strength of international institutions. A discretionary bargaining model of coordination is more likely to be successful when national leaders share a policy diagnosis that both cuts across economic issue areas and divides their own domestic political coalitions and governments. International organizations may facilitate policy coordination under a rule-based system through provision of resources to ease adjustment costs and rule clarification, and in a discretionary bargaining system by brokering, providing information and model building.