The FBI is the third level of law enforcement that pursues the player. The FBI will only appear when the player's wanted level reaches five stars, before the Army on six stars.
FBI Agents wear blue jackets with "FBI" printed on the back in nearly all of the 3D Universe games (excluding Liberty City Stories). In Grand Theft Auto: Vice City Stories, they wear black vests over differently colored t-shirts with "FBI" printed on the back with dark glasses and caps. The FBI agents are well armed in all appearances, and their vehicles are generally extremely fast. The FBI comes with four agents in each car, and since they are well armed and very accurate, they will kill the player extremely quickly if they have an open range. They carry MP5s in all of the 3D Universe games, except for Grand Theft Auto III, where this weapon is unavailable, and instead they carry AK-47s and pistols (when killed or encountered in a roadblock).
In GTA III and GTA Liberty City Stories, their headquarters is located in Torrington, Staunton Island, Liberty City. Strangely, in both games, there are no FBI vehicles near this building.
The CIA Agents (guarding the Shoreside Lift Bridge in Marked Man) and Liberty City Port Authority officers (in the hangar from Grand Theft Aero) share the same character polygon as the FBI Agents. However, the CIA Agents wear all black, while the Port Authority have different caps.
Some FBI agents speak with country accents, suggesting that most of the agents come from the countryside.
In the 10th Anniversary Edition, the FBI agents have had the lettering changed from FBI to FIB. This does not apply to the name of the FBI Car, however.
Grand Theft Auto: San Andreas
Some missions have FBI wielding Micro SMGs instead of SMGs. The same case is equivalent to the SWAT in missions wielding SMGs instead of Micro SMGs.
If the player clears their wanted level and manages to kill or hurt any agent on-screen, they will obtain a one-star wanted level as opposed to two like the regular police, SWAT, and military. However, killing or hurting another agent and other types of law enforcement will result in getting a two-star level.
Grand Theft Auto: Liberty City Stories
In the mobile version, the FBI agents have had the lettering changed from FBI to FIB, like the 10th Anniversary Edition of Grand Theft Auto III.
Grand Theft Auto: Vice City Stories
The FBI seem to be one of the most hostile in the 3D Universe, as their blockades will instantly blow up or heavily damage your car on sight. The best way to maneuver through a blockade is to get a bullet-proof car.