An international organization established in 1945 as successor to the League of Nations with the goal of working for peace, security, and cooperation among the nations of the world. Its permanent headquarters are in New York. The term “United Nations” was first used in a Declaration of the United Nations in January 1942, when representatives of 26 Allied nations pledged their governments to continue fighting together against the Axis powers, but it was only after further conferences held at Dumbarton Oaks, Washington, in 1944, and San Francisco in 1945 that representatives of 50 Allied countries signed the document, known as the Charter, setting up the new organization. The UN grew rapidly as former colonial territories became independent nations and applied for membership. In 2014 the organization had 193 members, most of the countries of the world.

In order to carry out its many functions, the UN is served by a wide range of organs and institutions. The six principal organs of the UN are the United Nations General Assembly (UNGA), the United Nations Security Council, the International Court of Justice, the Economic and Social Council (which deals with international economic, social, cultural, educational, health and related matters), the Trusteeship Council (which administers those territories held in trust by the UN), and the Secretariat, which is responsible for the general administration of the UN. The Secretariat is headed by the Secretary-General, who is appointed for a five-year renewable term by the General Assembly. There have been eight Secretary-Generals since the UN was founded: Trygve Lie (Norway), (1946–53); Dag Hammarskjöld (Sweden), (1953–61); U Thant (Burma), (1961–71); Kurt Waldheim (Austria), (1971–81); Javier Pérez de Cuéllar (Peru), (1981–92); Boutros Boutros-Ghali (Egypt), (1992–97); Kofi Annan (Ghana), (1997–2007); Ban Ki-moon (South Korea), (2007–16); and Antonio Gutiérrez (Portugal) from 2017. The UN is also served by 15 intergovernmental agencies known as the specialized agencies, dealing with economic and social questions. They include the International Monetary Fund (IMF), the United Nations Educational, Scientific and Cultural Organization (UNESCO), and the World Health Organization (WHO). Other organs which are part of the UN system include the United Nations Conference on Trade and Development (UNCTAD), and the Office of the United Nations High Commissioner for Refugees (UNHCR).