The design process for the United Nations headquarters formally began in February 1947, and a groundbreaking ceremony for the Secretariat Building occurred on September 14, 1948.

[4][9] West of the Secretariat Building is a circular pool with a decorative fountain in its center,[10][11] as well as a sculpture executed in 1964 by British artist Barbara Hepworth in memory of Secretary-General Dag Hammarskjöld.

[15] Outside of the UN headquarters, Robert Moses Playground is directly to the south, and Tudor City and the Ford Foundation Center for Social Justice are to the west.

[20] The Secretariat Building was designed in the International Style[2] by a team of ten architects working under planning director Wallace K.

[21][22] The Board of Design comprised Nikolai Bassov of the Soviet Union; Gaston Brunfaut of Belgium; Ernest Cormier of Canada; Le Corbusier of France; Liang Seu-cheng of China; Sven Markelius of Sweden; Oscar Niemeyer of Brazil; Howard Robertson of the United Kingdom; G. A. Soilleux of Australia; and Julio Vilamajó of Uruguay.

[45] The General Bronze Corporation manufactured and supplied the building with 5,400 individual windows, spandrel frames, louvers, and architectural metalwork.

[27][30] The reflective glass was chosen mainly as a means to reduce heat on the western elevation, which absorbed most of the sunlight during a typical workday.

[48][49] General Bronze Corporation manufactured the windows to meet the specifications of Harrison's design: "a curtain wall cantilevered two feet, nine inches, in front of the steel structure so that it formed a flush skin of blue-green Thermopane heat-absorbing glass, painted black on the inner face.

[49] The modern curtain walls are hung from the superstructure via outrigger plates, and there are projecting aluminum mullions similar to those on the original sash windows.

[30] According to Harrison, the marble walls not only allowed the Secretariat Building to be seen as a monument, but also reduced competition between staff members who wanted corner offices.

[66] In addition, the United Nations headquarters had a pneumatic mail system, with tubes connecting to a central collection point in the Secretariat Building.

[82] On floor 5 are employee amenities, including a health clinic and a passageway to a staff dining room above the adjacent Conference Building.

[66][74] The dining room was initially supposed to be an open-air terrace facing the East River, but it was partially enclosed due to pollution from a nearby power plant.

[30][88] The eastern side of the building was more desirable because it faced the East River, and higher-level diplomats needed large amounts of space for secretaries, filing cabinets, and other functions.

There are hot-water heating units beneath the windows, within the north and south walls of the building, and underneath the floor slab of the first story; in addition, there are steam heaters in the pipe galleries.

[65][93] The use of East River water precluded the need for a dedicated cooling tower, which would have required increasing the building's height and strengthening the superstructure.

[66][74][94] The suite was donated by the Austrian Chamber of Commerce and designed by Gerhard Karplus of New York City and Mr. and Mrs. Karl Mang of Vienna.

[95] In addition, floor 38 had a private switchboard and an office for the President of the United Nations General Assembly; most Secretariat employees were not allowed to visit this story.

[112][113][114] After much discussion, Harrison decided to select a design based on the proposals of two board members, Oscar Niemeyer and Le Corbusier.

[120][121] The same month, UN Secretary-General Trygve Lie and the architects began discussing ways to reduce construction costs by downsizing the headquarters.

[124] In April 1948, US President Harry S. Truman requested that the United States Congress approve an interest-free loan of US$65 million to fund construction.

[31][32] Le Corbusier insisted that the facade of the Secretariat Building contain brises soleil, or sun-breakers, even as Harrison argued that the feature would be not only expensive but also difficult to clean during the winter.

[144] The joint venture had started constructing the piers under the building by the end of January 1949,[145] and site excavations were completed the next month.

[152][153] New York Governor Thomas E. Dewey laid the headquarters' cornerstone on October 24, 1949, the fourth anniversary of the United Nations' founding.

[174] The next year, Secretary-General Dag Hammarskjöld proposed allocating US$635,000 to install automatic elevators in the Secretariat Building due to increasing labor costs.

[189][186] The mechanical systems were so outdated that the UN had to manufacture its own replacement parts,[52][190] and up to one quarter of the building's heat escaped through leaks in the curtain wall.

[192] Following the September 11 attacks in 2001, the Secretariat Building's curtain walls were covered with a green coating, which was intended to limit damage in case of a bombing.

[189] The UN selected Fumihiko Maki to design a building on the Moses site,[194] but the New York State Legislature refused to pass legislation in 2005 that would have allowed these plans to proceed.

The Secretariat Building would be renovated in four phases, each covering ten stories, and the UN would lease an equivalent amount of office space nearby.

[52][198] Prior to the start of the renovation, in 2008, Secretary-General Ban Ki-moon approved a pilot program to reduce heat emissions by raising temperatures throughout the building.