Comprehensive Nuclear-Test-Ban Treaty

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) was opened for signature at the United Nations in New York on 24 September 1996, after negotiations concluded in the Conference on Disarmament in Geneva. It prohibits "any nuclear weapon test explosion or any other nuclear explosion" in all environments — atmospheric, underwater, underground, and in outer space — extending the partial ban established by the 1963 Limited Test Ban Treaty to cover underground tests as well.

The treaty has not yet entered into force. Entry into force requires ratification by all 44 states listed in Annex 2 — countries that participated in the 1996 Conference on Disarmament session and possessed nuclear power or research reactors at that time. Several Annex 2 states have not ratified, including the United States, China, Iran, Israel, and Egypt, while India, Pakistan, and North Korea have neither signed nor ratified.

Despite not being in force, the CTBT has established a de facto international norm against nuclear testing. The Preparatory Commission for the CTBTO (CTBTO PrepCom), headquartered in Vienna, operates the International Monitoring System (IMS) — a global network of seismic, hydroacoustic, infrasound, and radionuclide stations designed to detect nuclear explosions anywhere on Earth. The IMS detected each of North Korea's announced nuclear tests (2006, 2009, 2013, two in 2016, and 2017).

Key features include:

• On-Site Inspection (OSI) provisions allowing intrusive verification once the treaty enters into force.
• An Executive Council and Technical Secretariat structure.
• A withdrawal clause permitting exit with six months' notice if "extraordinary events" jeopardize a state's supreme interests.

In November 2023, Russia revoked its 2000 ratification of the CTBT, though it stated it would continue to observe the testing moratorium so long as the United States does. The treaty remains a central instrument of the global nuclear nonproliferation architecture alongside the NPT.