In 2023, the Program on Nuclear Issues at the Center for Strategic and International Studies published a report titled Irreversibility in Nuclear Disarmament. In their introduction to this text, Heather Williams and Jessica Link remind readers that “nuclear ‘irreversibility’ is not a new challenge; it has been a component of nuclear arms control and disarmament efforts for decades.” They traced that the concept of irreversibility when discussing nuclear disarmament appeared for the first time as part of the vocabulary of the NPT in 2000 in the Review Conference Final Document. Since then, a diverse array of definitions of irreversibility have appeared, identifying different requirements, processes, and end-goals for IND.
Policymakers and analysts point to the diversity in approaches toward irreversibility as a challenge for conceptualising and operationalising IND. Participants in this dialogue concluded that diversity in how actors think about IND might not be an insurmountable obstacle per se. The international non-proliferation and disarmament regime functions with critical concepts that do not have a consensual or even definite meaning. Definitional ambiguity in the non-proliferation regime has been abused by governments but it has also provided opportunities to bring actors into the regime, strengthen commitments, and improve verification and monitoring mechanisms. Participants agreed, however, that crafting a shared vision of irreversibility is necessary to lay the foundations for successful multilateral works around IND.
Despite challenges and pitfalls, diversity can become an asset when conceptualising and promoting IND. Only through diversity will it be possible to achieve a shared understanding of irreversibility that is not another hurdle to fulfilling a pillar of the NPT. Favouring diversity could also have a more pragmatic result: it can lead to constructing a more comprehensive toolkit to promote, guarantee, and sustain disarmament. The benefit of diversity, thus, would be to generate a common baseline upon which to build policies, practices, and mechanisms for IND. To achieve this goal, then, it is necessary to include more voices into more in-depth discussions, particularly from non-nuclear-weapon states and developing countries. A possibility could be to have NNWS and Global South actors host meetings on IND as part of the NPT intersessional working group or as part of the working of different nuclear-weapon-free zones.
 Heather Williams and Jessica Link, “Introduction,” in Heather Williams, Jessica Link, and Joseph Rodgers (eds.), Irreversibility in Nuclear Disarmament, A Report of the CSIS Project on Nuclear Issues, Washington, D.C., Center for Strategic and International Studies, 2023, p. 1, in https://www.csis.org/analysis/irreversibility-nuclear-disarmament
 Stuart Casey-Maslen, Arms Control and Disarmament Law, Oxford, Oxford University Press, 2021, Chapter 3; Daniel Joyner, Interpreting the Nuclear Non-Proliferation Treaty, Oxford, Oxford University Press, 2011, pp. 21-22; Reid B. C. Pauly, “Deniability in the Nuclear Nonproliferation Regime: The Upside of the Dual-Use Dilemma,” International Studies Quarterly, vol. 66, 2022, sqab036, in https://doi.org/10.1093/isq/sqab036