The Federal Bureau of Investigation (FBI) is a governmental agency belonging to the United States Department of Justice that serves as both a federal criminal investigative body and an internal intelligence agency (counterintelligence). Also, it is the government agency responsible for investigating crimes on Indian Reservations in the United States under the Major Crimes Act. The branch has investigative jurisdiction over violations of more than 200 categories of federal crime.

The agency was established in 1908 as the Bureau of Investigation (BOI). Its name was changed to the Federal Bureau of Investigation (FBI) in 1935.

The agency headquarters is the J. Edgar Hoover Building, located in Washington, D.C.. The agency has fifty-six field offices located in major cities throughout the United States, and more than 400 resident agencies in lesser cities and areas across the nation. More than 50 international offices called "legal attachés" exist in U.S. embassies and consulates general worldwide.