The Federal Bureau of Investigation (FBI) is the domestic intelligence and security service of the United States, which simultaneously serves as the nation's prime Federal law enforcement organization. Operating under the jurisdiction of the U.S. Department of Justice, FBI is concurrently a member of the U.S. Intelligence Community and reports to both the Attorney General and the Director of National Intelligence. A lead U.S. counterterrorism, counterintelligence, and criminal investigative organization, FBI has jurisdiction over violations of more than 200 categories of federal crime.
Although many of FBI's functions are unique, its activities in support of national security are comparable to that of the British MI5 and the Russian FSB. Unlike the Central Intelligence Agency (CIA), which has no law enforcement authority and is focused on intelligence collection overseas, FBI is primarily a domestic agency, maintaining 56 field offices in major cities throughout the United States, and more than 400 resident agencies in lesser cities and areas across the nation. At an FBI field office, a senior-level FBI officer concurrently serves as the representative of the Director of National Intelligence (DNI).