How many sovereign states have successfully detonated nuclear weapons?

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, the Russian Federation (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 known to have nuclear weapons, though it maintains a policy of deliberate ambiguity regarding this (has not acknowledged it), 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 has approximately 80 nuclear warheads.

South Africa developed nuclear weapons but then disassembled its arsenal before joining the NPT. Nations that are known or thought to have nuclear weapons are sometimes referred to informally as the nuclear club.