The Federal Bureau of Investigation (FBI) is the primary investigative arm of the United States Department of Justice (DOJ), serving as both a federal criminal investigative body and a domestic intelligence agency. At present, the FBI has investigative jurisdiction over violations of more than 200 categories of federal crimes, making the FBI the de-facto lead law enforcement agency of the United States government. The motto of the bureau is "Fidelity, Bravery, Integrity".

In fiscal year 2006, the FBI's total budget was approximately $8.7 billion, including $495 million in program increases to enhance counter-terrorism, counterintelligence, cyber crime, information technology, security, forensics, training, and criminal programs.

It was established in 1908 as the Bureau of Investigation (BOI), and the name was changed to the FBI in 1935.

The FBI headquarters is in Washington, D.C., and there are also has 56 field offices located in major cities throughout the United States as well as over 400 resident agencies in smaller cities and towns across the nation, and more than 50 international offices, called "Legal Attachés", in U.S. embassies worldwide.