Frustrated by the abrogation of promises by nuclear weapons states to disarm, countries that have foregone nuclear weapons joined forces with key members of civil society in efforts that culminated in the Treaty on the Prohibition of Nuclear Weapons (TPNW). How did this initiative succeed-in defiance of the major powers - in changing the discourse around nuclear weapons? What roles did the various actors play, and how did the language of the treaty evolve? Answering these questions, Jean Krasno and Elisabeth Szeli provide a deeply researched account of the TPNW campaign, the negotiations, and the ongoing challenges of ratification and implementation.