Why should sovereign states obey international law? In this groundbreaking study Fernando Tesón argues that an overlapping respect for human rights has created a moral common ground among the countries of the world. It is this common set of values rather than self-interest that ultimately provides legitimacy to international law. Using the tools of moral philosophy Tesón analyzes the concepts of sovereignty, intervention, and national interest; the contributions of social contact theory, game theory, and feminist theory; and the puzzles of self-determination and group rights.