A field commission (or brevet) refers to either a Starfleet commissioned officer holding a higher rank temporarily, or, in some cases, personnel from outside Starfleet temporarily being granted a Starfleet rank for the purposes of completing a specific mission.
Under normal circumstances, those who receive a field commissions will wear the rank insignia to which they have been commissioned. In 2371, a system was in place to allow those receiving field commissions to wear provisional rank insignia, until the commissions could be confirmed by Starfleet Command.
A field commission is not to be confused with a battlefield promotion, in which the officer in question is promoted while deployed in combat.
- 2366 - Commander William Riker granted a field commission to Captain. (TNG episode: "The Best of Both Worlds")
- 2371 - Tom Paris, (offically an observer onboard the USS Voyager (NCC-74656)) granted a field commission to Lieutenant (j.g). (VOY episode: "Caretaker")
- 2371 - When stranded in the Delta Quadrant, several Maquis operatives were granted field commissions aboard Voyager. These included Chakotay (commissioned as Lieutenant Commander) and B'Elanna Torres (commissioned as Lieutenant (j.g). Upon Voyager's return to Federation space, in 2377, all of these provisional commissions were accepted by Starfleet Command. (VOY episode: "Caretaker"; VOY novel: Homecoming)
- 2375 - Colonel Kira Nerys of the Bajoran Militia granted a field to commission to commander. (DS9 episode: "When It Rains...")