The North Atlantic Treaty, also known as the Washington Treaty, forms the legal basis of, and is implemented by, the North Atlantic Treaty Organization (NATO). The treaty was signed in Washington, D.C., on 4 April 1949.
Background The treaty was signed in Washington, D.C., on 4 April 1949 by a committee which was chaired by US diplomat Theodore Achilles. Earlier secret talks had been held at the Pentagon between 22 March and 1 April 1948, of which Achilles said:
The talks lasted about two weeks and by the time they finished, it had been secretly agreed that there would be a treaty, and I had a draft of one in the bottom drawer of my safe. It was never shown to anyone except Jack [Hickerson]. I wish I had kept it, but when I left the Department in 1950, I dutifully left it in the safe and I have never been able to trace it in the archives. It drew heavily on the Rio Treaty, and a bit of the Brussels Treaty, which had not yet been signed, but of which we were being kept heavily supplied with drafts. The eventual North Atlantic Treaty had the general form, and a good bit of the language of my first draft, but with a number of important differences.
According to Achilles, another important author of the treaty was John D. Hickerson:
More than any human being Jack was responsible for the nature, content, and form of the Treaty...It was a one-man Hickerson treaty.
As a fundamental component of NATO, the North Atlantic Treaty is a product of the US' desire to avoid overextension at the end of World War II, and consequently pursue multilateralism in Europe. It is part of the US' collective defense arrangement with Western European powers, following a long and deliberative process. The treaty was created with an armed attack by the Soviet Union against Western Europe in mind, although the mutual self-defense clause was never invoked during the Cold War.
By signing the North Atlantic Treaty, parties are "determined to safeguard the freedom, common heritage and civilization of the peoples, founded on the principles of democracy, individual liberty and the rule of law."
Members
Founding members
The following twelve states signed the treaty and thus became the founding members of NATO. The following leaders signed the agreement as plenipotentiaries of their countries in Washington, D.C., on 4 April 1949: – Prime Minister and Foreign Minister Paul-Henri Spaak and Ambassador Baron – Secretary of State for External Affairs Lester B. Pearson and Ambassador H. H. Wrong – Foreign Minister Gustav Rasmussen and Ambassador Henrik Kauffmann – Foreign Minister Robert Schuman and Ambassador Henri Bonnet – Foreign Minister Bjarni Benediktsson and Ambassador Thor Thors – Foreign Minister Carlo Sforza and Ambassador Alberto Tarchiani – Foreign Minister Joseph Bech and Ambassador Hugues Le Gallais – Foreign Minister Dirk Stikker and Ambassador Eelco van Kleffens – Foreign Minister Halvard M. Lange and Ambassador Wilhelm von Munthe af Morgenstierne – Foreign Minister José Caeiro da Mata and Ambassador Pedro Teotónio Pereira – Foreign Secretary Ernest Bevin and Ambassador Oliver Franks – Secretary of State Dean Acheson
Non-founding members who joined before the dissolution of the Soviet Union
The following four states joined the treaty after the 12 founding states, but before the dissolution of the Soviet Union: (joined in 1952)Joined as Kingdom of Greece. (joined in 1952) (joined in 1955)Joined as West Germany. After reunification in 1990, the former East German territory became covered by NATO protection. (joined in 1982)
Members who joined after the dissolution of the Soviet Union The following 16 states joined the treaty after the dissolution of the Soviet Union: (joined in 1999) (joined in 1999) (joined in 1999) (joined in 2004) (joined in 2004) (joined in 2004) (joined in 2004) (joined in 2004) (joined in 2004) (joined in 2004) (joined in 2009) (joined in 2009) (joined in 2017) (joined in 2020) (joined in 2023) (joined in 2024)
Withdrawal No state has rescinded its membership, but some dependencies and jurisdictions of member states that had prior NATO mutual defense protection under Article 6 have not requested membership after becoming independent or handed over to non-NATO states, e.g.: (independence from the United Kingdom in 1960) (independence from France in 1962) (independence from the United Kingdom in 1964) north of the Tropic of Cancer (independence from the United Kingdom in 1973) (independence from the United Kingdom in 1981)
Provisions
Article 1 Article 1 of the treaty states that member parties "settle any international disputes in which they may be involved by peaceful means in such a manner that international peace and security, and justice, are not endangered, and to refrain in their international relations from the threat or use of force in any manner inconsistent with the purposes of the United Nations."
Members seek to promote stability and well-being in the North Atlantic area through preservation of peace and security in accordance with the Charter of the United Nations.
Article 2 Article 2 of the treaty stipulates that "The Parties will contribute toward the further development of peaceful and friendly international relations by strengthening their free institutions, by bringing about a better understanding of the principles upon which these institutions are founded, and by promoting conditions of stability and well-being. They will seek to eliminate conflict in their international economic policies and will encourage economic collaboration between any or all of them." This is sometimes referred to as the Canada Clause after Pearson pushed for its inclusion in the treaty. This included proposals for a trade council, cultural program, technological sharing, and an information program. Of those, only the latter two were passed. Nonetheless, it has been brought up by observers commenting on trade disputes between members.
Article 3
Article 3 of the treaty states that "In order more effectively to achieve the objectives of this Treaty, the Parties, separately and jointly, by means of continuous and effective self-help and mutual aid, will maintain and develop their individual and collective capacity to resist armed attack."
This was interpreted in 2022 as the basis for the target for a 2% GDP expenditure rule, which was established as a loose guideline in 2006. This metric was confirmed again during the 2014 Wales summit.
It has also been used as a core concept for a mandate to strengthen member resilience: the ability to resist and recover from major disasters, failures in infrastructure, or traditional armed attack. This commitment was first accepted during the 2016 Warsaw summit, and further reiterated and clarified due to the COVID-19 pandemic in 2021. In accordance with NATO documents, this has been understood to include seven key areas: Continuity of government during a crisis Energy and power grid infrastructure resilience Immigration control Food and water security Medical emergencies Resilient civil communications Effective transportation networks
Article 4 Article 4 is generally considered the starting point for major NATO operations, and therefore is intended for either emergencies or situations of urgency. It officially calls for consultation over military matters when "the territorial integrity, political independence or security of any of the parties is threatened." Upon its invocation, the issue is discussed in the North Atlantic Council, and can formally lead into a joint decision or action (logistic, military, or otherwise) on behalf of the Alliance.
Invocations
It has been invoked nine times as of 19 September 2025.
+ Article 4 invocations Nations Date Reason Outcome February 2003 Iraq War Operation Display Deterrence June 2012 Shootdown of a Turkish military jet by Syria Operation Active Fence October 2012 Syrian forces shelling Turkish cities , Turkishpress.com March 2014 Russian annexation of Crimea Deployment of forces in the Black Sea by Romania, Bulgaria, and TurkeyAid to the Ukrainian governmentCreation of NATO Enhanced Forward Presence July 2015 2015 Suruç bombing by ISISOther security issues along its southern bordertelegraph.co.uk: "Turkey calls for emergency Nato meeting to discuss Isil and PKK" , 26 July 2015nytimes.com: "Turkey and U.S. Plan to Create Syria 'Safe Zone' Free of ISIS" , 27 July 2015 Denunciation of the attack and reassessment of NATO assets in Turkey February 2020 Increasing tensions as part of the Northwestern Syria offensiveSyrian and Russian airstrikes on Turkish troopsAugmentation of Turkish air defences February 2022 Russian invasion of Ukraine Defensive build-upMatériel support to UkraineActivation of the NATO Response ForceSeptember 2025Russian drone incursion into PolandOperation Eastern SentrySeptember 2025Incursion of Russian fighter jets into Estonian airspace
Threatened invocations There have also been instances where Article 4 was not formally invoked, but instead threatened. In fact, this was viewed as one of the original intentions for Article 4: as a means to elevate issues and provide member nations a means of deterrence. For example, in November 2021, the Polish foreign ministry—along with Estonia, Lithuania, and Latvia—briefly considered triggering Article 4 due to the Belarusian migrant crisis, but it was not formally requested. On 28 December 2024, Swedish member of parliament and former minister of defense, Peter Hultqvist wanted the government to activate Article 4 in response to the 2024 Baltic Sea submarine cable disruptions and in September 2025, Denmark also considered it after unauthorised drone flights over airports and military bases in the country.
Article 5 The key section of the treaty is Article 5. Its commitment clause defines the casus foederis. It commits each member state to consider an armed attack against one member state, in the areas defined by Article 6, to be an armed attack against them all. Upon such attack, each member state is to assist by taking "such action as [the member state] deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area." The article has only been invoked once, but considered in a number of other cases.
Invocations September 11 attacks
Article 5 has been invoked only once in NATO history, after the September 11 attacks on the United States in 2001. Following the September 11 attacks, the Secretary General of NATO, George Robertson telephoned Colin Powell and said that declaring an Article 5 contingency would be a useful political statement for NATO to make. The United States indicated it had no interest in making such a request itself; however, it would not object to the council taking such action on its own.
Threatened invocations