CTBT

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is an international agreement that bans all nuclear explosions for both military and civilian purposes. It seeks to impede development of new nuclear weapons and to strengthen the global nuclear nonproliferation regime.

Open for signature on 24 September 1996 in New York, the treaty establishes a comprehensive prohibition on nuclear tests and sets out a verification regime designed to detect and deter violations. The treaty does not enter into force until it has been ratified by all 44 states that possess nuclear power or research reactors at Annex 2 of the treaty. As of 2024, not all of these states have deposited their instruments of ratification, so the treaty has not yet entered into force. Major holdouts include some of the world's largest nuclear powers.

The verification framework is led by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) Preparatory Commission, based in Vienna. It operates the International Monitoring System, a global network of seismic, hydroacoustic, infrasound, and radionuclide sensors, designed to detect nuclear explosions. Data collected by IMS stations is transmitted to the International Data Centre and is available to treaty members. The treaty also provides for on-site inspections if a decision by the CTBTO's Executive Council is made following a data-driven assessment and a positive vote by member states.

The CTBT remains a central element of global disarmament and nonproliferation efforts, though its ultimate entry into force remains unresolved. The CTBTO continues to expand verification capabilities and monitoring capacity in advance of possible entry into force.