Although the Member States of the United Nations (UN) unanimously endorsed the 'responsibility to protect' (R2P) principle in October 2005, debates continue about its scope, potential impact and how it might be operationalised. This article examines one strand of the wider efforts to turn the responsibility to protect into a workable international agenda, namely, the 'responsibility not to veto'. This is the idea that the permanent five members of the UN Security Council (P5) should agree not to use their veto power to block action in response to genocide and mass atrocities which would otherwise carry a majority in the Council and where their own vital security interests are not engaged. It has been promoted in a variety of international forums for nearly a decade but has not been adopted by the P5. We argue that this idea deserves support although we acknowledge that it addresses only one part of the wider conundrum of preventing mass atrocities. Its primary limitation is that the problem veto abstention is designed to solve – situations where potential rescuers are blocked by a (threat of ) P5 veto – has been a rare occurrence in contemporary world politics. The more common scenario has been that cases of mass atrocities have not generated sufficient political will to mobilise an international military response. Consequently, the responsibility not to veto must form part of a broader range of R2Pfriendly measures to help prevent mass atrocities and rescue their victims should they occur.