What is NATO?
The nutshell
NATO is a group of 32 countries that agree to defend each other. If one member country is attacked, the other members agree to help. The United Kingdom helped set NATO up in 1949.
Every fact on this page comes from official NATO texts and non-partisan explainers. Each source tag — like NATO — opens where a fact comes from.
The basics
What NATO is
NATO stands for the North Atlantic Treaty Organisation. It is an alliance — a group of countries that agree to work together for defence. NATO has 32 member countries in Europe and North America.NATO Its main office, or headquarters, is in Brussels, in Belgium.NATO
How NATO started
NATO was set up in 1949. Twelve countries signed the North Atlantic Treaty on 4 April 1949.NATO The United Kingdom was one of those twelve founding countries.HoC More countries have joined since, which is how the number grew to 32.
The main promise: Article 5
The most important rule in NATO is called Article 5. It says an armed attack on one member country is treated as an attack on the whole alliance.HoC The aim is that an attacker would face all the members together, not one country alone. Article 5 has been used only once, after the attacks on the United States in 2001.NATO
The UK and NATO
The UK Joint Delegation to NATO is the link between the UK government and NATO.GOV The UK government calls NATO the bedrock of the country's defence.GOV
- Supporters argue that the promise of collective defence has helped protect member countries from attack
- Article 5 means an attacker would face all 32 members at once, which supporters see as a strong deterrent
- Supporters note that NATO acts only when every member agrees, so no single country can commit the others alone
- Critics argue that NATO growing to include countries near Russia has added to tension in Europe
- Some critics say certain members have spent less on defence than the level members agreed to aim for
- Critics question whether every member would really send forces if Article 5 were ever used
The deep end6 min
What NATO is, and where it is based
NATO, the North Atlantic Treaty Organisation, is a defensive alliance of 32 member countries from Europe and North America. Its political headquarters sits in Brussels, in Belgium.NATO The House of Commons Library describes NATO as an alliance built on collective defence, which means the members agree to protect one another.HoC
Where NATO came from
Twelve countries signed the North Atlantic Treaty on 4 April 1949.NATO The founding members included the United Kingdom, the United States, France, Canada and eight others.HoC The alliance was formed after the Second World War, at the start of the period known as the Cold War. Membership has grown in stages since then, reaching 32 member countries.NATO
Article 5, and the one time it was used
Article 5 of the North Atlantic Treaty is the heart of the alliance. It says an armed attack on one member, in Europe or North America, is to be treated as an attack on the whole alliance.NATO Article 5 does not order a member country to go to war. Each member gives the help it judges necessary, which can include the use of armed force.NATO NATO has invoked Article 5 once in its history, after the attacks on the United States on 11 September 2001.NATO
The UK's place in NATO
The United Kingdom was one of the twelve countries that founded NATO in 1949.HoC Today the UK Joint Delegation to NATO acts as the link between the UK government and the alliance, and the UK government describes NATO as the bedrock of the country's defence.GOV