The North Atlantic Treaty Organization (NATO) is an intergovernmental military alliance of North American and European countries, including Canada as a founding member since 1949. NATO members commit to collective defence, meaning an attack on one member is considered an attack on all. Canada contributes military forces to NATO operations, hosts training exercises, and participates in alliance decision-making. While NATO is a federal international relations matter, municipalities may host military bases supporting NATO commitments, be affected by defence spending decisions, or engage with veterans and military families. NATO membership shapes Canada's defence policy and international security commitments.