Primarily focused on the theoretical aspects of international organization, this book provides an in-depth examination of competing theories through thematic chapters, asking, Do international organizations matter? What are their effects on international relations? Where do they fit into the international relations literature? How should we study them? This book addresses these questions by looking at four distinctions to be found in the theoretical literature on international organizations. The distinctions are those between sovereignty and globalization, between power and interdependence, between efficiency and ideas, and between regimes and institutions. These theories are then applied to specific international organizations, including the United Nations and other organizations that deal with issues including international and human security, human rights and humanitarian aid, the international political economy and development, and the global environment. Intended to fill the gap between introductory textbooks and primary sources of theory, this newly revised and updated edition of International Organization is useful for upper-level international relations courses with a significant emphasis on theory.