The Postman Always Rings Twice is a 1934 crime novel by James M. Cain.

The novel was quite successful and notorious upon publication, and is regarded as one of the more important crime novels of the 20th century. Fast-moving and brief (only about 100 pages long, depending on the edition), the novel's mix of sexuality and violence was startling in its time, and saw the book banned in Boston.[

It is also included in the Modern Library 100 Best Novels list.

It has been adapted as a motion picture five times. The 1946 version is probably the best known, and is regarded as an important film noir. It featured Lana Turner, John Garfield, Cecil Kellaway, Hume Cronyn, Leon Ames, and Audrey Totter. It was directed by Tay Garnett, with a score written by George Bassman and Erich Zeisl (the latter uncredited).[