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.
The Postman Always Rings Twice has been adapted into a film five times, an opera, and a play.