As of 2021, nine states possess nuclear weapons: Russia, US, China, France, UK, Pakistan, India, Israel, and North Korea. The most recent entrant into that nuclear club was North Korea, in 2006.

A few other states possessed nuclear weapons in the past but no longer do: in particular, some former Soviet republics gave up their inherited nuclear weapons after the Soviet Union collapsed, and South Africa built nuclear weapons but then dismantled them in 1991.

Other states have secretly explored nuclear weapon development or have been found in violation of the Nuclear Non-Proliferation Treaty. Some countries have more Breakout Capability than others-- both Japan and Iran have sufficient uranium and other resources to quickly develop nuclear weapons.