NATO (North Atlantic Treaty Organization) is an international military alliance consisting of 31 member states from Europe and North America. NATOs founding member countries were Belgium, Canada, Denmark, France, Iceland, Italy, Luxembourg, the Netherlands, Norway, Portugal, the United Kingdom, and the United States. Since then, 19 more countries have joined NATO through nine rounds of enlargement (in 1952, 1955, 1982, 1999, 2004, 2009, 2017, 2020, and 2023). The current NATO member countries, listed alphabetically, are:

• Albania
• Belgium
• Bulgaria
• Canada
• Croatia
• Czech Republic
• Denmark
• Estonia
• France
• Germany
• Greece
• Hungary
• Iceland
• Italy
• Latvia
• Lithuania
• Luxembourg
• Montenegro
• Netherlands
• North Macedonia
• Norway
• Poland
• Portugal
• Romania
• Slovakia
• Slovenia
• Spain
• Turkey
• United Kingdom
• United States

It is important to note that NATO membership is open to any "European State in a position to further the principles of this Treaty and to contribute to the security of the North Atlantic area". Any decision to invite a country to join the Alliance is taken by the North Atlantic Council, NATOs principal political decision-making body, on the basis of consensus among all Allies.