The legitimacy of humanitarian intervention has been contested for more than a century, yet pressure for such intervention persists. Normative evolution and institutional design have been closely linked since the first debates over humanitarian intervention more than a century ago. Three norms have competed in shaping state practice and the normative discourse: human rights, peace preservation, and sovereignty. The rebalancing of these norms over time, most recently as the state’s responsibility to protect, has reflected specific international institutional environments. The contemporary (...) legitimacy of humanitarian intervention is based on UN Security Council authorization of the use of force. Although the Security Council is often viewed as representative of great-power influence, international acceptance of its role is based on the role of non-permanent members and their support for the sovereignty norm. The current rebalanced norms supporting humanitarian intervention, institutional bias that protects state sovereignty, and the changing character of mass violence may undermine the tenuous contemporary legitimacy of humanitarian intervention. Normative adjustments and new institutional designs are required to insure the legitimacy of international action that protects populations against mass violence. (shrink)