Harry Ambrose Sylvester (January 19, 1908 – September 26, 1993) was an American short-story writer and novelist in the first half of the 20th century. His stories were published in popular magazines such as Collier's, Esquire, Columbia, and Commonweal. The most popular of his novels were Dearly Beloved (1942), Dayspring (1945), and Moon Gaffney (1947). He was asked to turn John Steinbeck's script for Alfred Hitchcock's Lifeboat (1944) into a short story. This version was published in Collier's in 1943, with Steinbeck and Hitchcock both receiving writing credits.