General · EdgepediaSeptember 17, 20266 min read

Comprehensive Nuclear-Test-Ban Treaty

The Comprehensive Nuclear-Test-Ban Treaty (CTBT) is a multilateral treaty that prohibits all nuclear weapon test explosions and any other nuclear explosions, for both civilian and military purposes, in all environments: underground, underwater, in the atmosphere, and in space. It was adopted by the United Nations General Assembly on 10 September 1996 and opened for signature in New York on 24 September 1996, but it has not entered into force because ratification by all 44 states listed in its Annex 2 is required first.¹^•²

Key fact	Detail
Core obligation	Each State Party agrees not to carry out, encourage, or support any nuclear weapon test explosion or other nuclear explosion, and to prohibit and prevent such activities under its jurisdiction or control³
Adopted / opened for signature	General Assembly resolution A/RES/50/245, 10 September 1996; opened for signature 24 September 1996¹
Entry into force	180 days after all 44 Annex 2 states ratify; ratification by nine of them is still needed⁴
Status	187 signatures and 178 ratifications as of August 2025⁵
Verification	International Monitoring System of 321 stations and 16 laboratories in 89 countries, using seismic, hydroacoustic, infrasound, and radionuclide technologies⁶
Organization	CTBTO Preparatory Commission, established by a resolution of 19 November 1996, headquartered in Vienna³
Testing record	Over 2,000 nuclear tests had taken place when the treaty opened for signature; fewer than a dozen have occurred since, including six by North Korea⁷

Background and negotiation

The treaty concluded decades of on-and-off efforts that began in the late 1950s. The 1963 Treaty Banning Nuclear Weapon Tests in the Atmosphere, in Outer Space and Under Water, known as the Partial or Limited Test-Ban Treaty (LTBT), banned nuclear explosions in the atmosphere, outer space, and underwater but left underground testing permitted; the 1968 Nuclear Non-Proliferation Treaty (NPT) reaffirmed in its preamble the commitment to seek the discontinuance of all nuclear test explosions, and the 1974 Threshold Test Ban Treaty limited underground weapons tests to yields of 150 kilotons.²^•⁸ The Conference on Disarmament began substantive negotiations on a comprehensive treaty in January 1994 through an Ad Hoc Committee.⁹

When negotiations stalled, Australia requested on 22 August 1996 that the General Assembly take up the treaty text directly, and the Assembly adopted it in September. India declined to support the text, citing its misgivings about the entry-into-force provision, which it considered unprecedented in multilateral practice and contrary to customary international law, and the treaty's failure to include a commitment by the nuclear-weapon states to eliminate nuclear weapons within a time-bound framework.⁹

Structure and obligations

The treaty consists of a preamble, 17 articles, two annexes, and a Protocol with two further annexes. Article I contains the basic obligation not to carry out, encourage, or support any nuclear explosion. Article II establishes the Comprehensive Nuclear-Test-Ban Treaty Organization in Vienna. Article IV defines the global verification regime, and Article XIV governs entry into force. The treaty is of unlimited duration and is not subject to reservations.³

According to the preamble, limiting the development and qualitative improvement of nuclear weapons, together with bringing an end to the creation of advanced new types of such weapons, makes a test ban an effective step toward nuclear disarmament and non-proliferation.¹⁰

Verification regime

Monitoring. The International Monitoring System (IMS), when complete, will consist of 321 monitoring stations and 16 radionuclide laboratories hosted by 89 countries. It uses four complementary technologies: 50 primary and 120 auxiliary seismic stations to detect underground tests through ground shockwaves, 11 hydroacoustic stations to detect sound waves in the oceans, 60 infrasound stations to listen for ultra-low-frequency atmospheric sound waves, and 80 radionuclide stations to detect radioactive particles or gases, which are the only direct evidence that an explosion was nuclear. Around 90 percent of the 337 designated facilities are operational.⁶^•¹¹

Data analysis. The International Data Centre in Vienna receives data around the clock from the IMS network and distributes it to member states in both raw and analyzed form; states that cannot interpret the data themselves may request special processing from the center.¹²^•⁸ When North Korea conducted its declared nuclear test explosions, member states received information on the location, magnitude, time, and depth of the events within two hours.¹²

On-site inspection. On-site inspection is the final verification measure and can be conducted only once the treaty is in force, at the request of a State Party, when IMS data indicate a suspected breach. The regime also includes a consultation and clarification process, under which a state receiving a clarification request has 48 hours to respond, and voluntary confidence-building measures: states are asked to notify the CTBTO of any chemical explosion of 300 tonnes or more of TNT-equivalent blasting material on their territory, so that large mining blasts are not mistaken for nuclear tests.⁴^•¹²

The system has detected all six of North Korea's declared nuclear tests between 2006 and 2017, along with earthquakes, volcanic eruptions, meteor strikes, and non-nuclear explosions such as the 2020 Beirut blast. Its data also support tsunami warnings, tracking of radioactive releases from accidents, and research on subjects from whale behavior to monsoon timing.⁶

Entry into force and current status

The treaty will enter into force 180 days after all 44 states listed in Annex 2 have ratified. These are the states that formally participated in the final stage of negotiation in the Conference on Disarmament in 1996 and possessed nuclear power or research reactors at that time.¹³ As of 2025, ratification by nine Annex 2 states is still needed: China, Egypt, India, Iran, Israel, North Korea, Pakistan, the Russian Federation, and the United States. China and the United States signed on 24 September 1996 but have not ratified; India, Pakistan, and North Korea have neither signed nor ratified.⁴^•⁷

Russia ratified the treaty on 30 June 2000 but revoked its ratification on 8 November 2023.⁴ Article XIV provides that if the treaty has not entered into force three years after its opening for signature, a conference may be held at the request of a majority of ratifying states to facilitate entry into force; such conferences have been held, and a 2025 report counted 35 of the 44 Annex 2 ratifications at that time.⁹^•¹⁴

Although not in force, the treaty has helped establish a strong global norm against nuclear testing. When it opened for signature, more than 2,000 nuclear tests had taken place; since then there have been fewer than a dozen, including six by North Korea. Executive Secretary Robert Floyd of the CTBTO warned in 2026 that if the United States, Russia, or any other nation resumed testing, other nations would follow, and that the IMS can detect even a relatively small nuclear explosion anywhere in the world.⁷ In late 2025 both the United States and Russia threatened to resume nuclear testing, and the treaty and the de facto global moratorium face renewed pressure three decades after its conclusion.⁷^•¹⁵

References

Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 25, 2026 · Edited: Sep 30, 2026; Oct 25, 2026