The Justice Department is the federal government's law enforcement and legal arm. It prosecutes federal crimes through the ninety-plus U.S. Attorneys' offices around the country, represents the United States in civil litigation, and enforces federal civil rights, antitrust, and environmental laws.

The Attorney General, the nation's chief law enforcement officer, oversees a sprawling set of law enforcement agencies including the FBI, the Drug Enforcement Administration, the Bureau of Alcohol, Tobacco, Firearms and Explosives, and the U.S. Marshals Service, along with the federal Bureau of Prisons, which houses more than 150,000 inmates.

The department also supervises the federal immigration court system through its Executive Office for Immigration Review, an arrangement that places immigration judges inside the executive branch rather than the independent judiciary, a structural quirk that frequently surprises people learning about it for the first time.