In 2005 the member states of the United Nations recognized a “responsibility to protect” (“R2P”) victims of mass atrocities such as genocide, war crimes, and crimes against humanity. They acknowledged a special role for the U.N. Security Council in responding to these atrocities, including potentially authorizing military action using its extensive powers under Chapter VII of the U.N. Charter. However, the Council has very rarely been able to agree on appropriate action, and the five permanent Council members (“P5”), most notably (...) China and Russia, have often vetoed or threatened to veto Council resolutions authorizing R2P action. The article argues that the veto poses a major impediment to the Council acting on its R2P responsibilities, and that to resolve it, the P5, and all U.N. member states, need to agree on a common ethical approach. The article proposes such an approach based on ethical concepts that are widely endorsed by states, especially in the U.N. Charter and the Universal Declaration of Human Rights, and explores its implications for legal and ethical controversies relating to the role of the Council, its obligations under R2P, and proposed reforms of the veto. (shrink)