A chronology of key events:
1949 April - Twelve states - Belgium, Canada, Denmark, France, Britain, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal and the United States - sign the North Atlantic Treaty in Washington DC.
Nato's first supreme commander, Dwight Eisenhower
1950 - US General Dwight Eisenhower appointed supreme Nato commander.
1952 - Greece and Turkey join the alliance.
1955 - West Germany joins Nato; the Soviet Union and eight Eastern European states respond by forming the Warsaw Pact.
1966 - French President Charles de Gaulle announces France's intention to withdraw from Nato's military structure in protest at the dominance of US commanders.
1967 - Nato's new headquarters opened in Brussels.
1982 - Spain joins Nato.
1990 - Nato and Warsaw Pact states sign the Conventional Armed Forces in Europe treaty (CFE) and publish a joint declaration on non-aggression.
Britain's Lord Ismay, Nato's first secretary-general
1991 - Warsaw Pact is dissolved; Nato sets up the North Atlantic Cooperation Council as a forum for consultations between Nato members, East European states and the former Soviet republics.
1992 - Nato announces its readiness to support peacekeeping activities in the former Yugoslavia.
1993 - Nato agrees to offer former Warsaw Pact members limited associations with the alliance in the form of the Partnership for Peace programme.
1995 - Nato embarks on its first-ever military operation by launching a campaign of air strikes against Bosnian Serb positions to force the Bosnian Serbs to negotiate a peace settlement; Nato deploys thousands of troops - the Implementation Force (Ifor) - to monitor and enforce a ceasefire in Bosnia.
1997 - Ifor is replaced by a smaller force called the Stabilisation Force (Sfor); Nato and Russia sign the Founding Act to establish a framework for security cooperation.
Nato-Russia Permanent Joint Council set up to give Russia "a voice but no veto".
1999 - The Czech Republic, Hungary and Poland become the first former Soviet bloc states to join Nato, taking the alliance's borders some 400 miles towards Russia.
1999 - Nato begins an 11-week campaign of air strikes against Yugoslavia over Kosovo without UN approval; former British defence secretary George Robertson becomes secretary-general.
2001 - Disarmament operations in the former Yugoslav Republic of Macedonia.
2001 September - After 11 September attacks on targets in the US, Secretary-General Robertson invokes Article Five of the alliance's constitution spelling out that an attack on one is seen as an attack on all. However, Washington chooses not to involve Nato in the US-led military campaign which follows.
Nato hit China's Belgrade embassy in 1999, souring Sino-US ties
2002 May - Russian, Nato foreign ministers agree to set up Nato-Russia Council, in which Russia and Nato countries will have equal role in decision-making on policy to counter terrorism and other security threats.
2002 July - Secretary-General George Robertson visits Ukraine. He says further political, economic and military reforms are necessary before Ukraine can join Nato.
2002 November - Seven countries - Lithuania, Estonia, Latvia, Bulgaria, Romania, Slovakia and Slovenia - invited to join alliance at summit in Prague.
2003 February - France, Germany and Belgium temporarily block US move to offer military support to Turkey in event of war in Iraq. They say it amounts to military planning and thus could undermine diplomatic efforts to avoid conflict.
2003 June - Nato defence ministers agree to radical overhaul of alliance's military operation. Command structure streamlined to enable deployment of lighter, more flexible forces.
2003 August - Nato takes control of the International Security Assistance Force (Isaf) in Afghanistan, its first major operation outside Europe.
Kabul 2003: Nato takes on its first major mission outside Europe
2003 October - Nato launches 9,000-member rapid-reaction force which can be deployed anywhere in the world at short notice.
2003 October - US ambassador to Nato says Franco-German plan to set up independent European military planning HQ is threat to Nato's future. EU leaders seek to allay US fears, saying European defence policy intended to complement, not rival, Nato.
2004 January - Jaap de Hoop Scheffer succeeds George Robertson as secretary-general.
2004 March - Bulgaria, Estonia, Lithuania, Latvia, Romania, Slovakia and Slovenia formally welcomed in Washington as new members.
2004 April - Nato signs agreements establishing Russian military liaison offices at Nato HQ.
2004 December - Nato hands over peacekeeping duties in Bosnia to a new European Union-led force, Eufor.
International Court of Justice says it has no jurisdiction in a case brought by Serbia and Montenegro challenging the legality of Nato's 1999 bombing of the then Yugoslavia during the Kosovo crisis.
2005 December - Nato foreign ministers agree to expand the alliance's role in Afghanistan. Plans include the deployment of thousands more troops in the south.
2006 31 July - Nato takes over command in southern Afghanistan from the US-led coalition.
2006 September - Troops engage in fierce fighting with the Taleban in southern Afghanistan.
2008 April - Bucharest Summit invites Albania and Croatia to join Nato. Decisions on Georgia and Ukraine deferred until December. Postpones Macedonian membership until dispute with Greece settled.
2008 May - Nato members Germany, Slovakia, Latvia, Lithuania, Italy and Spain to staff and fund new cyber defence centre in Estonia, which last year blamed Russia for weeks of attacks on its internet structure.
2008 August - Nato says there can be no "business as usual" with Moscow unless it pulls its troops out of Georgia. Russia halts all military co-operation with Nato.
2008 September - Nato delegation visits Georgia to express solidarity following war with Russia. Secretary-General Jaap de Hoop Scheffer criticises EU-brokered ceasefire deal for allowing more Russian forces to remain in breakaway regions of Abkhazia and South Ossetia.
2009 March - Nato says that high-level contacts with Russia will be resumed after Nato's 60th anniversary summit.
French President Nicolas Sarkozy announces that France is to return to Nato's military command.
2009 April - Nato's 60th anniversary summit. Albania and Croatia are formally inducted, increasing membership to 28.
2009 July - Anders Fogh Rasmussen takes over as secretary-general.
2010 October - Nato foreign and defence ministers meet to discuss a proposed new "strategic concept" or mission statement for the alliance, drawn up by Secretary General Anders Fogh Rasmussen.
2010 November - New "strategic concept" is agreed at Nato summit in Lisbon. The meeting also reaches agreement on establishment of missile defence shield for Europe - reaching new level of understanding with Russia in the process - and endorses 2014 as date for withdrawal of Nato troops from Afghanistan.
2011 March - UN Security Council approves imposition of no-fly zone over Libya to protect civilians from Col Gaddafi's forces. Nato agrees to take on responsibility for enforcing the no-fly zone.
2011 July - Nato Secretary-General Anders Fogh Rasmussen says the Libya mssions is extended for another three months and will continue to be extended for as long as necessary. He says the Gaddafi government should not try to "wait Nato out".
Nato deploys peacekeepers in the north of Kosovo after a border post with Serbia was burnt down and a Kosovo policeman killed in an attack by local local Serbian nationalists who reject Kosovo independence.
2011 October - Nato formally ends its Libya mission after the fall of the last Gaddafi stronghold, and offers to help the new government with security matters.
2011 November - Pakistan halts Nato ground supplies to Afghanistan after a Nato airstrike kills 24 of its troops.
2011 December - The International Court of Justice rules that Greece was wrong to have blocked Macedonia's Nato membership application in 2008. The ruling will make it harder for Greece to oppose another Macedonian bid.
2012 February - A leaked Nato reports says the Afghan Taliban are helped by Pakistani security services and enjoy wide public support, causing a rift with the Pakistani government and raising questions about the organisation's continuing role in Afghanistan.