The Gallery's campus includes the original neoclassical West Building designed by John Russell Pope, which is linked underground to the modern East Building, designed by I. M. Pei, and the 6.1-acre (25,000 m2) Sculpture Garden. The Gallery often presents temporary special exhibitions spanning the world and the history of art. It is one of the largest museums in North America.
Pittsburgh banker (and Treasury Secretary from 1921 until 1932) Andrew W. Mellon began gathering a private collection of old master paintings and sculptures during World War I. During the late 1920s, Mellon decided to direct his collecting efforts towards the establishment of a new national gallery for the United States.
In 1930, partly for tax reasons, Mellon formed the A. W. Mellon Educational and Charitable Trust, which was to be the legal owner of works intended for the gallery. In 1930–1931, the Trust made its first major acquisition, 21 paintings from the Hermitage Museum in St. Petersburg as part of the Soviet sale of Hermitage paintings, including such masterpieces as Raphael's Alba Madonna, Titian's Venus with a Mirror, and Jan van Eyck's Annunciation.
In 1929 Mellon had initiated contact with the recently appointed Secretary of the Smithsonian Institution, Charles Greeley Abbot. Mellon was appointed in 1931 as a Commissioner of the Institution's National Gallery of Art. When the director of the Gallery retired, Mellon asked Abbot not to appoint a successor, as he proposed to endow a new building with funds for expansion of the collections.
However, Mellon's trial for tax evasion, centering on the Trust and the Hermitage paintings, caused the plan to be modified. In 1935, Mellon announced in The Washington Star, his intention to establish a new gallery for old masters, separate from the Smithsonian. When asked by Abbot, he explained that the project was in the hands of the Trust and that its decisions were partly dependent on "the attitude of the Government towards the gift".
In January 1937, Mellon formally offered to create the new Gallery. On his birthday, 24 March 1937, an Act of Congress accepted the collection and building funds (provided through the Trust), and approved the construction of a museum on the National Mall.
The new gallery was to be effectively self-governing, not controlled by the Smithsonian, but took the old name "National Gallery of Art" while the Smithsonian's gallery would be renamed the "National Collection of Fine Arts" (now the Smithsonian American Art Museum).