Pacta sunt servanda is one of the central principles of international relations and international law. States are expected to uphold their treaties, and they do so in the vast majority of cases.2 But there is an important set of cases in which they do not. Consider two recent examples. Since 2014, Russia has violated the Intermediate‐Range Nuclear Forces (INF) Treaty by developing and testing new ground‐launched cruise missiles.3 In 2018, Canada breached the Single Convention on Narcotic Drugs by legalizing the recreational use of cannabis.4 Although both Russia and Canada clearly violated international law, there seems to be a normative difference between these two cases. Whereas Russia violated the INF Treaty for reasons of national interest and military advantage, Canada violated the Single Convention in order to implement a law that a large majority of its citizens supports. This article explores justifications for repudiating treaties, or for abrogating them on extra‐legal or political grounds.5 When, if ever, is it justifiable for a state to repudiate a treaty?