When is it right to go to war? The most persuasive answer to this question has always been 'in self-defense'. In a penetrating new analysis, bringing together moral philosophy, political science, and law, David Rodin shows what's wrong with this answer. He proposes a comprehensive new theory of the right of self-defense which resolves many of the perplexing questions that have dogged both jurists and moral philosophers. By applying the theory of self-defense to international relations, Rodin produces a far-reaching critique of the canonical Just War theory. The simple analogy between self-defense and national defense - between the individual and the state - needs to be fundamentally rethought, and with it many of the basic elements of international law and the ethics of international relations.