association of 10 countries ( Belgium, France, Germany, Greece (Greece, history of), Italy, Luxembourg, The Netherlands (Netherlands, The), Portugal, Spain, and the United Kingdom) that operates as a forum for the coordination of matters of European security and defense. It contributed to the creation of the North Atlantic Treaty Organization (NATO) and works in cooperation with that organization. The WEU became the primary defense institution of the European Union in the 1990s, though it gave up that role in 2001.

The WEU grew out of the Brussels Treaty of 1948—an agreement between Belgium, France, Luxembourg, The Netherlands, and the United Kingdom to provide for collective defense and to facilitate cooperation in economic, social, and cultural matters. NATO and the Council of Europe (Europe, Council of), both of which were formed in 1949, developed out of that framework. In 1954 the Brussels Treaty was strengthened and modified to include West Germany and Italy, to end the occupation of West Germany, and to include West Germany in NATO; and the WEU came into being on May 6, 1955. In 1960 the activities of committees for social and cultural affairs were transferred to the Council of Europe. In 1984 the union was “reactivated” and a new agenda established: it recognized the significance of U.S. arms to the defense of Europe and resolved to increase regional military cooperation.

In 1988 Portugal and Spain joined the union; Greece joined in 1992. There are also six associate members (Czech Republic, Hungary, Iceland, Norway, Poland, and Turkey), five observer countries (Austria, Denmark, Finland, Ireland, and Sweden), and seven associate partners (Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia, and Slovenia).

The WEU is administered by a council consisting of the ministers of foreign affairs and of defense of the member countries. The council is responsible for policy formulation and is headed by a secretary-general. Three internal agencies are also involved. The assembly of the WEU, which has a number of permanent committees (political defense, technological and aerospace, rules of procedure and privileges, and parliamentary and public relations), consists of the delegates of the member countries to the Parliamentary Assembly of the Council of Europe; it meets at least twice each year (normally in Paris). Headquarters of the WEU are in Brussels.