The vitality of the NPT after 50

The most inclusive security treaty in the world, the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) turned 50 in 2020. Our special issue takes stock of the NPT’s vitality after these five decades. In this introduction, we emphasize the need to distinguish between the treaty instrument and the larger nuclear nonproliferation regime. Next, we consider a recent development that may represent a serious impending shock which could weaken the NPT: dramatic changes in the treaty’s legal and normative landscape. Then, we assess vitality of the NPT in light of current concerns, arguing that norm contestation can be healthy for international regimes and calls for the death of the NPT are premature. Finally, we review the contributions of our special issue authors, highlighting the significant differences among them, and embedding them in ongoing research on the NPT.