Ace in the Hole, also known as The Big Carnival, is a 1951 American satirical drama film directed, produced, and co-written by Billy Wilder. The film stars Kirk Douglas as a cynical, disgraced reporter who creates a media circus surrounding a man trapped in a cave in rural New Mexico to try to regain a job on a major newspaper. The film co-stars Jan Sterling and features Robert Arthur and Porter Hall.

The film marked a series of firsts for Wilder: it was the first time he was involved in a project as a writer, producer, and director; his first film after parting ways with his long-time writing partner Charles Brackett; and his first film to be a critical and commercial failure, though it has since been reappraised as one of his major works.

Without consulting Wilder, Paramount Pictures executive Y. Frank Freeman changed the title to The Big Carnival just prior to its release. Early television broadcasts retained that title, but when aired by Turner Classic Movies – and when released on DVD by The Criterion Collection in July 2007 – it reverted to Ace in the Hole.

In 2017, the film was selected for preservation in the United States National Film Registry by the Library of Congress as being "culturally, historically, or aesthetically significant".

The film is sometimes referred to as a film noir, though some critics dispute this.