The Hitchhiker's Guide to the Galaxy is a comedy science fiction franchise created by Douglas Adams. Originally a 1978 radio comedy broadcast on BBC Radio 4, it was later adapted to other formats, including novels, stage shows, comic books, a 1981 TV series, a 1984 text adventure game, and 2005 feature film.

The Hitchhiker's Guide to the Galaxy is an international multimedia phenomenon; the novels are the most widely distributed, having been translated into more than 30 languages by 2005. The first novel, The Hitchhiker's Guide to the Galaxy (1979), has been ranked fourth on the BBC's The Big Read poll. The sixth novel, And Another Thing..., was written by Eoin Colfer with additional unpublished material by Douglas Adams. In 2017, BBC Radio 4 announced a 40th-anniversary celebration with Dirk Maggs, one of the original producers, in charge. The first of six new episodes was broadcast on 8 March 2018.

The broad narrative of Hitchhiker follows the misadventures of the last surviving man, Arthur Dent, following the demolition of the Earth by a Vogon constructor fleet to make way for a hyperspace bypass. Dent is rescued from Earth's destruction by Ford Prefect—a human-like alien writer for the eccentric, electronic travel guide The Hitchhiker's Guide to the Galaxy—by hitchhiking onto a passing Vogon spacecraft. Following his rescue, Dent explores the galaxy with Prefect and encounters Trillian, another human who had been taken from Earth (before its destruction) by the self-centred President of the Galaxy Zaphod Beeblebrox and the depressed Marvin the Paranoid Android. Certain narrative details were changed among the various adaptations.