Book excerpt: The North Atlantic Treaty Organization (NATO) is a military alliance established by the signing of the North Atlantic Treaty on April 4, 1949. The treaty was signed by Belgium, the Netherlands, Luxemburg, France, United Kingdom, United States, Canada, Portugal, Italy, Norway, Denmark and Iceland. Today there are a total of 26 countries that belong to NATO. The A to Z of NATO and Other International Security Organizations covers the Atlantic Alliance's origins, structure and organization through a chronology, an introductory essay, a bibliography, and over 1,000 cross-referenced dictionary entries on its Secretaries-Generals, its Supreme Allied Commanders-Europe, plus all affiliated organizations created to enhance NATO's reach in a broader Euro-Atlantic security architecture (e.g., North Atlantic Consultative Council, Euro-Atlantic Partnership Council, NATO-Russia Charter; NATO-Ukraine Charter, and NATO-Mediterranean Dialogue Partners). This book also covers other related regional organizations with security responsibilities in Europe and worldwide where they interact with NATO, either currently (e.g. ANZUS, ASEAN, European Union, Organization of African Unity, Organization of American States, Organization on Security and Cooperation in Europe, and United Nations) or in the past (e.g. CENTO, European Defence Community, SEATO, Warsaw Pact, and Western European Union).