Whichever position one holds on the virtue and practicality of international action to protect humans from imminent peril, it is indisputable that the past few decades have seen a proliferation of mechanisms, institutions and practices aimed at improving protection. This has gone hand in hand with a global decline in both armed conflict and mass atrocities. Through at least eight distinct but connected streams of practice, we have seen the codification of norms of acceptable behaviour, the establishment of responsibilities for third party states and international institutions, and the emergence of a range of practices aimed towards the protection of vulnerable populations. As a result, mass violence today is typically met with complex – if not always entirely effective – responses from a range of different types of actors. Nevertheless, international practices of protection have improved markedly over the past few decades, contributing to an overall decline in both the incidence and lethality of atrocity crimes. The most important point is that this all remains unfinished business. Not only are there a number of political issues left to address, we have barely begun to scratch the surface of the practical issues connected to implementation. Questions of which strategies offer most protection in what kinds of circumstances will need to be addressed if the promise of protecting people globally is to be turned into a lasting reality.