Eight sovereign states have publicly announced successful detonation of nuclear weapons. Five are considered to be nuclear-weapon states (NWS) under the terms of the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). In order of acquisition of nuclear weapons, these are the United States, Russia (the successor of the former Soviet Union), the United Kingdom, France, and China. Of these, the three NATO members, the UK, US, and France, are sometimes termed the P3.

Other states that possess nuclear weapons are India, Pakistan, and North Korea. Since the NPT entered into force in 1970, these three states were not parties to the Treaty and have conducted overt nuclear tests. North Korea had been a party to the NPT but withdrew in 2003.

Israel is also generally understood to have nuclear weapons, but does not acknowledge it, maintaining a policy of deliberate ambiguity. Israel is estimated to possess somewhere between 75 and 400 nuclear warheads. One possible motivation for nuclear ambiguity is deterrence with minimum political cost.

States that formerly possessed nuclear weapons are South Africa (developed nuclear weapons but then disassembled its arsenal before joining the NPT) and the former Soviet republics of Belarus, Kazakhstan, and Ukraine, whose weapons were transferred to Russia.

According to Stockholm International Peace Research Institute (SIPRI), the worldwide total inventory of nuclear weapons as of 2021 stood at 13,080. Around 30% of these are deployed with operational forces, and more than 90% are owned by either Russia or the United States.