The Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO) grew from a long campaign to close the last legal gap in nuclear restraint: a global, verifiable ban on all nuclear explosions .

After partial limits in 1963 and regional bans later, negotiations at the Conference on Disarmament yielded a draft treaty that the U.N. General Assembly adopted in September 1996, opening for signatures on September 24. Because entry into force required 44 named Annex 2 states with nuclear expertise to ratify it, governments created a Preparatory Commission in November 1996 to build, test, and provisionally operate a verification regime before the treaty legally began. The result was the Vienna-based CTBTO Preparatory Commission, which today runs the system that would underpin a future treaty in f

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