Precommitment Regimes for Intervention: Supplementing the Security Council Allen Buchanan and Robert O. Keohane* A s global governance institutions proliferate and become more powerful, their legitimacy is subject to ever sharper scrutiny. Yet what legitimacy means in this context and how it is to be ascertained are often unclear. In a previous paper in this journal, we offered a general account of the legitimacy of such institutions and a set of standards for determining when they are legiti- mate.  In this paper we focus on the legitimacy of the UN Security Council as an institution for making decisions concerning the use of military force across state borders. The context for this topic has changed over the last decade as a result of the ongoing development of the responsibility to protect (RtoP) doctrine and extensive discussions about it in the United Nations. Yet the mostly widely accepted proposals for RtoP still require Security Council authorization for force- ful intervention, and strictly limit the conditions under which such intervention may take place. The world currently lacks reliable multilateral arrangements both to prevent humanitarian disasters and to protect fragile democratic governments against coups and other violent attempts to overthrow them. We are particularly inter- ested in the protection of fragile democracies. It is a valid question whether demo- cratic publics should rely on the Security Council, with its particular composition and permanent member veto, to serve as their principal external guarantor. We argue that the Security Council is a legitimate institution for making these decisions, but that it does not possess unconditional exclusive legitimacy. That is, under some conditions, multilateral coercive intervention to resolve a *We are grateful for comments on earlier versions of this paper by Charles Beitz, Curtis Bradley, Michael Doyle, Laurence Helfer, Andrew Hurrell, Richard Steinberg, and Laura Valentini, and to three anonymous referees. Edward Luck was especially helpful at an early stage in the development of our ideas. Ethics & International Affairs, , no.  (), pp. –. ©  Carnegie Council for Ethics in International Affairs doi:./S 41