The Exorcist is a 1971 horror novel written by American writer William Peter Blatty and published by Harper & Row. The book details the demonic possession of eleven-year-old Regan MacNeil, the daughter of a famous actress, and the two priests who attempt to exorcise the demon. The novel was the basis of a highly successful film adaptation released two years later, whose screenplay was also written and produced by Blatty. More movies and books were eventually added to The Exorcist franchise.

Horror is a genre of fiction that is intended to disturb, frighten or scare. Horror is often divided into the sub-genres of psychological horror and supernatural horror, which are in the realm of speculative fiction. Literary historian J. A. Cuddon, in 1984, defined the horror story as "a piece of fiction in prose of variable length... which shocks, or even frightens the reader, or perhaps induces a feeling of repulsion or loathing". Horror intends to create an eerie and frightening atmosphere for the reader. Often the central menace of a work of horror fiction can be interpreted as a metaphor for larger fears of a society.