The Robert F. Kennedy Department of Justice Building, sometimes called Main Justice, is the headquarters of the United States Department of Justice. It houses Department of Justice offices, including the office of the United States attorney general. The building was completed in 1935. In 2001, it was renamed after Robert F. Kennedy, the 64th U.S. attorney general.

The building is located in Washington, D.C. at 950 Pennsylvania Avenue NW, on a trapezoidal lot on the block bounded by Pennsylvania Avenue to the north, Constitution Avenue to the south, 9th Street to the east, and 10th Street NW to the west, in the Federal Triangle. It is located west of the National Archives Building, east of the Internal Revenue Service Building, north of the National Mall, and south of the J. Edgar Hoover Building. The building is owned by the General Services Administration. It comprises seven floors and 1.2 million sq ft (110,000 m²).

The Office of the Attorney General was created by the 1st United States Congress by the Judiciary Act of 1789. In 1792, the Congress made the Attorney General a Cabinet-level post.

In 1870, President Ulysses S. Grant signed the bill creating the United States Department of Justice. There was not yet a permanent home for either the Attorney General or the Justice Department, and each had occupied a succession of temporary spaces in federal government buildings and privately owned office buildings. While plans to provide the department with its own building were developed as early as 1910, it was not until the late 1920s that significant progress was made toward this goal.

In 1908 and in 1928, Congress authorized the purchase of land in what is now known as the Federal Triangle for departmental offices. The authorization was part of a wave of government construction; the 1926 Public Buildings Act permitted the government to hire private architects for the design of federal buildings, which led to large-scale construction of public buildings, including the development of the 70 acre Federal Triangle site between the Capitol and the White House. Treasury Secretary Andrew W. Mellon and the Board of Architectural Consultants, composed of leading architects and headed by Edward H. Bennett of the Chicago architectural firm of Bennett, Parsons & Frost, developed design guidelines for the site. Under Bennett's direction, each member of the board designed one of the buildings in the Federal Triangle complex to "provide each government agency or bureau with a building that would address its functional needs, while combining the individual buildings into a harmonious, monumental overall design expressive of the dignity and authority of the federal government."

Milton Bennett Medary of the Philadelphia firm Zantzinger, Borie & Medary was selected as the architect for the Department of Justice Building; upon Medary's death in 1929, the project was taken over by his two partners Charles L. Borie Jr. and Clarence C. Zantzinger.

In 1930, Congress appropriated $10 million for the construction of a permanent Department of Justice headquarters in the Federal Triangle. The building was constructed from 1931 to 1934. Upon completion in 1935, the building finally provided a headquarters for the Attorney General and Department of Justice. One percent of the cost of its construction was for art; between 1935 and 1941, 68 murals were painted in the building (an example of New Deal art).

In 1966, the Department of Justice building was listed on the National Register of Historic Places as part of the Pennsylvania Avenue National Historic Site.