What is NATO?

A Transatlantic Alliance

The North Atlantic Treaty Organisation (NATO) was formed in 1949 with the signing of the North Atlantic Treaty in Washington. The treaty created an alliance of ten European and two North American states – the UK, Belgium, Canada, Denmark, France, Iceland, Italy, Luxemburg, the Netherlands, Norway, Portugal and the United States. It was formed to ensure their collective security and preservation and intended to counter the perceived threat from the then Soviet Union.

Article 5: An attack on one is an attack on all

At the heart of the Washington Treaty is Article 5. This states that an armed attack against one shall be considered an attack against them all.

It is important to note that Article 5 does not necessarily commit an ally to a military response. Rather, that they will assist the party or parties attacked "such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area."

Article 5 was invoked for the first time the day after the 11 September 2001 attacks in America.

Membership: 32 countries are part of NATO

NATO has seen several periods of expansion. Greece and Turkey were the first to join the founding 12 nations in 1952. Finland joined the Alliance on 4 April 2023 and Sweden became the 32nd member on 7 March 2024. More information on their accession can be found in Commons Library briefing NATO enlargement: Sweden and Finland.

How can countries join the Alliance?

Article 10 of the Washington Treaty sets out the membership requirements. Any European state may be invited by unanimous agreement to “further the principles” of the Treaty and to “contribute to the security of the North Atlantic Area.” NATO often says it has “open door policy”.

Who will join next?

Currently only Bosnia and Herzegovina is participating in the Membership Action Plan (MAP). This is the programme by which NATO supports an aspiring country prepare for possible future membership. It was launched in 1999.

There is no set duration for participation in the MAP as the requirements will differ for each country. The Republic of North Macedonia, for example, had been participating in the MAP since 1999 before formally joining NATO in 2020.

At the 2008 Bucharest Summit, Allied leaders agreed that Georgia and Ukraine will one day become members, though differences among Allies at the time meant they stopped short of inviting them to begin the MAP process.

Georgia was invited to participate in the meeting with the leaders at NATO’s summit in Madrid in June 2022.

At its summit in Vilnius in July 2023, NATO reaffirmed the commitment made in 2008 that Ukraine “will become a member” of the Alliance. Further discussion of Ukraine’s potential membership is set out in Commons Library briefing NATO enlargement: Ukraine.

How are decisions made?

Major decisions are approved at heads of government and state summits, held over one or two years. In between these summits, the foreign and defence ministers of Allies meet regularly. All decisions are made by consensus.

The North Atlantic Council (NAC) is the principal political decision-making body at NATO and each member country has a seat on the council. It meets at least weekly and is chaired by the Secretary General. The top military position, the Supreme Allied Commander Europe, is filled by an American, who is also the Commander of US European Command.

How is NATO funded?

NATO is funded by Allies both directly and indirectly. Direct contributions are made to NATO budgets and programmes on an agreed cost-share formula, based on Gross National Income. This is the principle of “common funding” and finances NATO’s principal budgets.

Indirect funding is where allies commit capabilities or troops to a military operation. On these occasions the member state bears the costs themselves.

What is the 2% target?

Discussions about NATO funding between Allies or in the press are generally less about the direct funding of NATO as an institution, and more about whether allies are fulfilling the agreed 2% target.

The 2% target was set at the 2006 Riga Summit. Member states agreed that 2% of a member’s gross domestic product (GDP) should go towards defence expenditure, and that 20% of defence expenditure should go towards the development and acquisition of equipment. It is a target, not a requirement.

Allies made an "enduring commitment to invest at least 2%" of GDP annually on defence at the Vilnius summit in 2024, adding that in many cases "expenditure beyond 2% of GDP will be needed in order to remedy existing shortfalls and meet the requirements across all domains arising from a more contested security order."

Does NATO have its own armed forces?

No. Each member contributes forces and equipment to specific operations or exercises.

NATO does own and operate some capabilities of its own, for example AWACS early warning radar aircraft.

2022: A new Strategic Concept

NATO adopted a new Strategic Concept at its summit in Madrid in June 2022. The concept will “define the security challenges facing the Alliance and outline the political and military tasks NATO will carry out to address them.”

Much has changed since the current Strategic Concept was adopted in 2010, when NATO was still leading operations in Afghanistan. Since then, NATO has refocused on the Euro-Atlantic area, hybrid and cyber warfare have been discussed at length, while China merited inclusion in the 2021 Brussels Summit communiqué.

What is the role of the NATO Parliamentary Assembly?

The NATO Parliamentary Assembly is independent of NATO and institutionally separate to it. However, it provides a link between NATO and the legislative bodies of NATO members. The UK has 18 seats in the Assembly. Library paper The NATO Parliamentary Assembly and UK delegations explains the purpose of the Assembly and the role of the UK delegation.

The Parliamentary Assembly's committees draft reports and policy recommendations examining all security and policy challenges confronting Allied countries. Library paper NATO Parliamentary Assembly: Reports of the 2021 annual session.

The attached paper expands on some of the questions above and also explores why NATO was involved in Afghanistan when it is a "North Atlantic" alliance and NATO's policy on nuclear weapons.