The Non-Proliferation Treaty (NPT) is an international treaty opened for signature on July 1, 1968, and entered into force on March 5, 1970. It was negotiated between 1965 and 1968 by the Eighteen Nation Committee on Disarmament to prevent the spread of nuclear weapons and technology, promote the peaceful use of nuclear energy, and further the goal of nuclear disarmament. The problem it addressed was the growing risk of widespread nuclear weapons technology in the 1960s.
The NPT works on a central bargain among its 191 States Parties, built on three pillars: non-proliferation, disarmament, and peaceful use of nuclear energy. It distinguishes between Nuclear-Weapon States (NWS)—the United States, Russia, the United Kingdom, France, and China, defined as those that exploded a nuclear device before January 1, 1967—and Non-Nuclear-Weapon States (NNWS). Under Article I, NWS agree not to transfer nuclear weapons or technology to any state, while under Article II, NNWS agree not to acquire or develop nuclear weapons. Article IV acknowledges the "inalienable right" of all parties to research and use nuclear energy for non-weapons purposes. The mechanism for verifying compliance is through the International Atomic Energy Agency (IAEA), which is tasked by Article III with inspecting NNWS nuclear facilities via comprehensive safeguards agreements.
The NPT is connected to the IAEA, which serves as its international safeguards inspectorate. The treaty was originally set for 25 years but was extended indefinitely at a review conference in May 1995. The treaty is reviewed every five years in Review Conferences, with the most recent one held in August 2022. India, Israel, Pakistan, and South Sudan have never joined the NPT. North Korea joined in 1985 but withdrew in 2003. The core provisions and the distinction between NWS and NNWS have stayed the same since its inception.