The Postman Always Rings Twice is a 1934 crime novel by American writer James M. Cain. The novel was successful and notorious upon publication. It is considered one of the most outstanding crime novels of the 20th century. The novel's mix of sexuality and violence was startling in its time and caused it to be banned in Boston.

Crime fiction, detective story, murder mystery, mystery novel, and police novel are terms used to describe narratives that centre on criminal acts and especially on the investigation, either by an amateur or a professional detective, of a crime, often a murder. It is usually distinguished from mainstream fiction and other genres such as historical fiction or science fiction, but the boundaries are indistinct. Crime fiction has several subgenres, including detective fiction, courtroom drama, hard-boiled fiction, and legal thrillers. Most crime drama focuses on crime investigation and does not feature the courtroom. Suspense and mystery are key elements that are nearly ubiquitous to the genre.