Sovereignty and the nation-state, cornerstones of the Westphalian system, have been eroded in fact and attacked in principle because what goes on inside states – that is, their internal governance – often matters intensely to other members of the international system. But who has the right or the legitimacy to violate another state’s sovereignty, and for what purposes? Is there a source of international legitimacy that does not itself depend on the existence and strength of sovereign nation-states? If not, doesn’t the attack on sovereignty become a self-contradictory enterprise? This chapter addresses this set of interrelated problems.