The United Nations faces unprecedented opportunities as well as heightened expectations in the wake of the Cold War. With as yet unmet challenges throughout the world, the limits to UN power and effectiveness are being realized.From regional conflicts to areas of environmental degradation, the UN's success will depend on the way in which three dilemmas are resolved--the tensions between sovereignty and the reality of its erosion, between demands for global governance and the weakness of UN institutions (as well as the reluctance of states to commit), and between the need for leadership and the diffusion of power. The authors explore these dilemmas in the context of the UN's historical evolution, including its experience with peacekeeping, peacemaking, and environmentally sustainabledevelopment. They also consider the role of various actors in the UN system, from major powers (especially the United States), small and middle powers, coalitions, and nongovernmental organizations, to the six secretaries-general. The need for institutional reforms and specific proposals for reform are examined.Because multilateral diplomacy is now the norm rather than the exception in world politics, the UN is more central than ever. This new text places the UN at the center of the entirely new set of dilemmas now emerging in world politics.