International organizations have proliferated in recent decades. Virtually every issue of broad international concern is the subject of an international agreement that is administered by an international organization. Broad powers are delegated to some of these international agents, many of which exercise significant discretion and authority. International courts with broad jurisdiction and hundreds of more specialized judicial organs have been established to interpret a rapidly expanding body of international law. The organizational capacity of international governance has increased, while the capacity of domestic governance has declined in a range of failed states and contested territories. Meanwhile, the depth of policy coordination demanded by international agreements has led to an unprecedented level of international policy activism by some of the leading international organizations, including the IMF, the WTO, and the EU. Given the importance of what international organizations do, it is increasingly important to understand how international organizations actually work.Most of our theoretical models of international organizations are based on their formal attributes rather than on their behavior. Formal rules are important, of course, and generally set the parameters within which informal interactions take place, but shared expectations and extra-legal practices often modify or overrule written provisions. As a result, models based on legal provisions can be misleading. For example, there are numerous international organizations in which votes are never taken, or are almost always unanimous; nevertheless, analyses of their governance often focus on the equilibria of majority voting games. Since the game being played does not involve building minimum winning coalitions, however, voting models based on majority voting can shed little light on the degree of influence that powerful countries exert over decision making, or on the practical limits of that influence. Similarly, procedural models of EU legislation assume that the game being played follows the legal procedures prescribed in the EU treaties; but this is often not the Rev Int