The United Nations headquarters complex on Manhattan's East River was officially dedicated on September 21, 1957, representing the formal completion of a project that began in the late 1940s to establish a permanent site for the global organization in New York City. Background and planning After the UN's founding in 1945, member states sought a permanent headquarters. In 1946 the United Nations General Assembly accepted an offer from the United States to provide a suitable site in New York. A riverside parcel in the Turtle Bay neighborhood of Manhattan was selected; the land was acquired and set aside for the project by the United Nations and the City of New York. An international team of architects, led by Wallace K. Harrison and including luminaries such as Le Corbusier and Oscar Niemeyer as part of an advisory board, produced the master plan and designs for the complex. Construction began in the late 1940s and continued through the 1950s. Construction and features The headquarters complex comprises several principal structures: the Secretariat Building, an internationalist modernist high-rise that served as the administrative center; the General Assembly Hall, a large domed assembly chamber designed for plenary meetings of all member states; and the Conference Building and other supporting facilities. Materials and labor were sourced internationally at times, and furnishings and artworks were contributed by member states as gestures of cooperation. Though portions of the complex were in use earlier, the formal dedication ceremony in September 1957 celebrated the official completion of the site as envisioned by the UN and its architects. The complex became the focal point for diplomatic activity in New York and a symbol of postwar multilateralism. Significance and legacy The dedication of the UN headquarters signaled the United Nations' establishment of a permanent, centralized seat of international diplomacy outside of Europe. Over the following decades the complex hosted General Assembly sessions, Security Council meetings, diplomatic conferences, and visits by heads of state and government. Architecturally, the site is notable as an example of mid-20th-century international modernism executed through an international collaboration. The site has undergone multiple renovations and security upgrades since 1957 to meet changing needs and standards. Preservation efforts have aimed to maintain the complex's architectural character while updating infrastructure. Today the United Nations headquarters remains both a working center for international diplomacy and a public symbol of the postwar international order. Notes on dates and usage While the dedication took place on September 21, 1957, parts of the headquarters had been occupied or used prior to that date as individual buildings were completed. Sources differ in emphasis between the dates when specific structures opened and the later formal dedication of the entire complex; the September 21, 1957, date is widely cited for the official dedication of the completed headquarters on the East River site.