The North Atlantic Treaty Organization (NATO, ; French: Organisation du traité de l'Atlantique nord, OTAN), also called the North Atlantic Alliance, is an intergovernmental military alliance between 30 member states, 28 of which are in Europe and the other 2 being part of North America. Established in the aftermath of World War II, the organization implements the North Atlantic Treaty, signed 4 April 1949.NATO constitutes a system of collective security, whereby its independent member states agree to mutual defense in response to an attack by any external party. It was established during the Cold War in response to the threat posed by the Soviet Union. The alliance has remained in place since the end of the Cold War, and has been involved in military operations in the Balkans, the Middle East, South Asia, and Africa. The NATO headquarters is located in Brussels, Belgium, while the headquarters of Allied Command Operations is near Mons, Belgium. The organization's motto is "animus in consulendo liber" (Latin for "A mind unfettered in deliberation").Since its founding, the admission of new member states has increased the alliance from the original 12 countries to 30. The most recent member state to be added to NATO was North Macedonia on 27 March 2020. NATO currently recognizes Bosnia and Herzegovina, Georgia, and Ukraine as aspiring members. Enlargement has led to tensions with non-member Russia, with Russian president Vladimir Putin demanding that NATO provide legal guarantees that it would stop expanding east (to countries such as Ukraine, Georgia or Moldova).

An additional 20 countries participate in NATO's Partnership for Peace programme, with 15 other countries involved in institutionalized dialogue programmes. The combined military spending of all NATO members in 2020 constituted over 57 per cent of the global nominal total. Members agreed that their aim is to reach or maintain the target defence spending of at least 2 per cent of their GDP by 2024.