In the past decade several countries have joined the world's rank of nuclear powers.
Some are located in unstable or tense regions, while others appear to lack the mutual understanding which helped prevent a nuclear exchange during the Cold War.
Several countries are either not members of the 1970 Non-Proliferation Treaty (NPT) designed to stop the spread of nuclear technology, or have withdrawn from it. Others have ignored the Comprehensive Test Ban Treaty (CTBT).
Use this guide to find out more about existing and emerging nuclear powers.