The most dramatic normative development of our time-comparable to the Nuremberg trials and the 1948 Convention on Genocide in the immediate aftermath of World War II-relates to the 'responsibility to protect', the title of the 2001 report from the International Commission on Intervention and State Sovereignty. It no longer is necessary to finesse the tensions between sovereignty and human rights in the UN Charter; they can now be confronted because sovereignty no longer implies the license to kill. This essay outlines the origins of the R2P idea, describes the background factors in the 1990s that paved the way for the advancement of this norm by norm entrepreneurs, champions, and brokers. It continues with an account of the process by which the ICISS arrived at its landmark report, a description of the sustained engagement with the R2P agenda from 2001, when the ICISS report was published, to its adoption at the 2005 World Summit. The essay concludes with a sketch of the tasks and challenges that lie ahead to move R2P from a norm to a template for policy and action.