In this article, we examined empirically the levels of cooperative behavior of nations inside and outside of intergovernmental organizations (IGOs), across types of IGOs (global, regional, “high politics,” “low politics”) and across types of nations (measured by relative size and level of economic development). We first confirmed the conventional view that foreign policy cooperation inside and outside IGOs is substantially different in each instance, but we also discovered significant differences in cooperation among the various types of IGOs. The low politics and the global IGOs showed particularly high levels of cooperation, but the regional organizations did not. The national attributes of the participating states proved not to be very useful in distinguishing the level of cooperation inside the various IGOs. Instead, knowing the type of intergovernmental organization seems more important in understanding interstate cooperation than knowing the type of state. The theoretical implications of these results are discussed throughout the article.