Although it is not part of the career development program in the FBI, some agents volunteer for service as an undercover agent (UCA). All UCAs are volunteers, and there is no special compensation for performing these duties. Generally, UCAs must have a solid investigative background before being considered for such work and also receive the full support of their superiors. Their undercover activities may take place in the office territory to which they are assigned or another field office. Volunteers for this program are evaluated for their expertise and psychological suitability. Special training programs are also available at [the FBI training complex at Quantico, Virginia] to teach agents the tricks of pulling off an undercover assignment. [Undercover operatives have to be good actors.]
The vast majority of undercover operations are criminal in nature, but intelligence-directed undercover operations also take place. Generally, undercover assignments fall into one of two categories. Group II operations can be approved by the Special Agent in Charge of the field division, with the concurrence of the local U.S. Attorney. Group IIs, as they are called, still require careful coordination and planning, but generally they are less sensitive, less dangerous, or shorter term, and less costly than other types of operations.
Group I undercover operations are the opposite. They may be dangerous, elaborate, lengthy, technically challenging, involve prominent personages, be very costly, or have foreign aspects involved. This group requires painstaking planning, substantial amounts of documentation, a lot of coordination, and minute review by a panel of senior FBI Headquarters and Department of Justice officials.
Perhaps the most legendary FBI Group I undercover operation was ABSCAM, a political corruption investigation that resulted in the conviction of members of Congress in the 1980s. Probably the most well known Group I operation was that of Special Agent Joe Pistone, who infiltrated the La Cosa Nostra (Mafia) with devastating results to the mobsters. So successful was Pistone in his role that he carried it out for years and was on the verge of becoming a "made guy" when the operation was terminated. His exploits were recounted in the book and movie that bears his undercover name, Donnie Brasco.
Joseph W. Koletar, The FBI Career Guide