Sister Act is a 1992 American comedy film directed by Emile Ardolino and written by Paul Rudnick (as Joseph Howard). It stars Whoopi Goldberg as a lounge singer forced to join a convent after being placed in a witness protection program. It also features Maggie Smith, Kathy Najimy, Wendy Makkena, Mary Wickes, and Harvey Keitel.

Sister Act was one of the most financially successful comedies of the early 1990s, grossing $231 million worldwide against a $31 million budget. The film spawned a franchise, which consists of the 1993 sequel Sister Act 2: Back in the Habit and a musical adaptation, which premiered in 2006. A third film is in development for Disney+

In 1968, Deloris Wilson is a young Catholic school student, who is less than serious about her studies, greatly embarrassing her nun teachers.

Twenty-four years later, in 1992, Deloris is a lounge singer in Reno, Nevada, performing as Deloris Van Cartier. After she witnesses her gangster boyfriend Vince LaRocca execute an informant, police lieutenant Eddie Souther places her in witness protection. She is brought to Saint Katherine's Convent in Saint Katherine's Parish, in a run-down neighborhood in San Francisco. Deloris initially objects, then relents.

The head nun of St. Katherine's, "Reverend Mother", also objects to taking Deloris in but Monsignor O'Hara, the local parish priest, convinces her to go along with it as the police will pay the failing convent a good sum of money to do so. Disguised as "Sister Mary Clarence", Deloris initially has difficulty dealing with the rigid and simple convent life but befriends the other nuns, (Sister Mary Patrick, the elderly Sister Mary Lazarus and the Novice Sister Mary Robert). One night, after a poorly attended Sunday Mass, with a lackluster performance from the convent choir, led by Mary Lazarus, Deloris sneaks out to a bar, followed by Mary Patrick and Mary Robert. They are caught by the Reverend Mother, who orders Deloris join the struggling choir. With her singing experience, Deloris is elected their director and transforms the choir.

At the next Sunday Mass, Deloris leads the much-improved choir in a traditional hymn, then shifts into a combined Gospel and Rock and Roll interpretation. Although Reverend Mother is infuriated, Monsignor O'Hara congratulates the choir for their unorthodox performance as new people were attracted to the service. Convinced by Deloris, he allows the nuns to clean the church and the neighborhood. Their singing and efforts to revitalize the neighborhood attract media attention, and the parish starts to thrive.

Souther chastises Deloris for nearly being exposed on national television as Vince has placed a bounty on her head. She assures him she will try to keep a lower profile and Souther attends a Mass. The nun's choir continues to amaze parishioners and visitors, especially with a rendition of "My Guy" – rewritten and performed as "My God".