Billy Costigan, a young man from a crook family, wants to do redeem the Costigan family by joining the cops. However, the cops see him as the perfect mole because of his crook family, so they send him undercover to the Irish Mob. Meanwhile, Frank Costello, the mob boss, sends in Colin Sullivan to become a cop for the opposite purpose. Both get caught up in their double lives and become obsessed with finding the other mole, as does Costello and Queenan, the heads of each side.

Martin Scorsese wanted to shoot the film in Boston, where the story is set. But due to concerns on setting up production and politics, the producers chose New York City to double for Boston because of the state's 15% tax credit. The bulk of the movie was shot in New York City while a six week shooting schedule was split in two for Boston, shooting the first half in June and the second half in August. After the success of this film, Massachusetts created a 25% tax credit for filmmaking.

Dignam:
This is unbelievable. Who put the fuckin' cameras in this place?


Police Camera Tech:
Who the fuck are you?


Dignam:
I'm the guy who does his job. You must be the other guy.

Continuity: When Billy visits Madolyn active window of Microsoft Anti Spyware on her monitor disappears and appears in different shots.

Written by Mick Jagger and Keith Richards
Performed by The Rolling Stones
By Arrangement with ABKCO Music & Records, Inc.