The Diamond as Big as the Ritz is a novella by novelist F. Scott Fitzgerald. It was first published in the June 1922 issue of The Smart Set magazine, and was included in Fitzgerald's 1922 short story collection Tales of the Jazz Age. Much of the story is set in Montana, a setting that may have been inspired by the summer that Fitzgerald spent near White Sulphur Springs, Montana in 1915.

Orson Welles adapted the story into a radio play in 1945 and another version was presented three times on the program Escape between 1947 and 1949.

A teleplay version was broadcast on Kraft Theatre in 1955. The story's sisters, Kismine and Jasmine, were portrayed by Lee Remick and Elizabeth Montgomery, who were unknowns of 20 and 22 at the time.

Mickey Mouse No. 47 (Apr./May 1956) contains a retelling of Fitzgerald's story under the title "The Mystery of Diamond Mountain", scripted by William F. Nolan and Charles Beaumont and illustrated by Paul Murry. Jimmy Buffett recounts the story in the song "Diamond As Big As The Ritz" from his 1995 album Barometer Soup.

Famous novells of the author F. S. Fitzgerald: "This Side of Paradise", "The Beautiful and Damned", "The Great Gatsby", "Tender Is the Night", "The Last Tycoon", "The Diamond as Big as the Ritz", "May Day", "The Rich Boy".