By entering into force on January 22, 2021, did the Treaty on the Prohibition of Nuclear Weapons (TPNW) ban nuclear weapons? From a legal perspective, the scope of the treaty does not reach beyond its members, all of whom already committed years ago not to acquire nuclear weapons, through the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). Yet, the international campaign led by a group of players, the most visible undoubtedly being the International Campaign to Abolish Nuclear Weapons (ICAN), asserts that nuclear weapons are “outlawed”. In particular, ICAN builds on this development to legitimize its action and chart a course that is no doubt necessary to secure its future and improve the image of the TPNW. At the same time, this NGO is driving a strategy to delegitimize nuclear weapons and stigmatize a number of States among those that have chosen to base their security on nuclear deterrence. This study aims to examine the challenges inherent in implementing the TPNW and the mechanisms involved in its use by ICAN.