This paper is an attempt to establish a legitimate basis for humanitarian intervention in a world of nominally sovereign states. I do this from two perspectives. First, I examine the legal discussions regarding such intervention, and I argue that a norm of justified intervention can be found in the UN Charter, the Universal Declaration of Human Rights and human rights covenants, as well as developing practice. Second, I examine the moral legitimacy of such actions. Specifically, I argue that beyond whatever basis may be present in international law for human rights and intervention to protect those rights, one can find a foundation for such rights in the very nature of the state system. Further, I argue that sovereignty cannot be a basis to prevent humanitarian intervention because the responsibilities which accrue to states mean that human rights must be seen as a part of the definition of sovereignty, rather than in opposition to it. In addition, within the concept of sovereignty, there is not only a right for the international community to violate international boundaries on behalf of human rights, but an obligation to do so.