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".
The FBI headquarters is in Washington, D.C., and there are also 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. (wikipedia)

From the moment of its birth in 1908 as the Justice Department's "Bureau of Investigation," a key part of the FBI's mission has been to suppress political dissent. In the early years they used deportations and the career-destroying Palmer raids to target union leaders and communists. Burglary, blacklisting, infiltration, and disruption became standard operating procedure. Later, when the Supreme Court ruled that the Smith Act specifically could not be used to target communists, the FBI took it undercover, developing its "counterintelligence" program dubbed COINTELPRO. In the words of then-director J. Edgar Hoover, COINTELPRO was designed to "expose, disrupt, misdirect, discredit, or otherwise neutralize" groups whose views the FBI deemed threatening to the status quo. (judibari.org)