There are eight sovereign states that have successfully detonated 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 (successor state to the Soviet Union), the United Kingdom, France, and China.

Since the NPT entered into force in 1970, three states that were not parties to the Treaty have conducted nuclear tests, namely India, Pakistan, and North Korea. North Korea had been a party to the NPT but withdrew in 2003. Israel is also widely believed to have nuclear weapons, though it maintains a policy of deliberate ambiguity regarding this, and is not known definitively to have conducted a nuclear test. According to the Stockholm International Peace Research Institute's SIPRI Yearbook of 2014, Israel is estimated to have approximately 80 nuclear warheads. Furthermore, according to Bulletin of the Atomic Scientists Nuclear Notebook 2014, the total number of nuclear weapons is estimated at 10,144.

South Africa has the unique status of a nation that developed nuclear weapons but then disassembled its arsenal before joining the NPT. This means that there are three European countries, one country in the Americas, four Asian countries, zero Oceanian countries and zero African countries which are known to possess nuclear weapons. Nations that are known or believed to possess nuclear weapons are sometimes referred to informally as the nuclear club.