The North Atlantic Treaty Organization (NATO ; ; ), also called the North Atlantic Alliance, is an intergovernmental military alliance based on the North Atlantic Treaty which was signed on 4 April 1949. The organization constitutes a system of collective defence whereby its member states agree to mutual defense in response to an attack by any external party. NATO's headquarters are located in Haren, Brussels, Belgium, where the Supreme Allied Commander also resides. Belgium is one of the 28 member states across North America and Europe, the newest of which, Albania and Croatia, joined in April 2009. An additional 22 countries participate in NATO's Partnership for Peace program, with 15 other countries involved in institutionalized dialogue programmes. The combined military spending of all NATO members constitutes over 70 percent of the global total. Members' defense spending is supposed to amount to 2 percent of GDP.

The domain .nato was a top-level domain (TLD) in the Domain Name System (DNS) of the Internet. The domain was added in the late 1980s by the Network Information Center for the use of NATO, the North Atlantic Treaty Organization, based on the rationale that none of the then existing top-level domains adequately reflected its status as an international organization. Soon after this addition, however, Paul Mockapetris, the designer of the DNS, suggested to NATO representatives that nato.int would be a better choice. The TLD .int was created for the use of international organizations, and NATO switch to using nato.int. Without use, the TLD nato was deleted in July 1996.