The Hitchhiker's Guide to the Galaxy, a science fiction comedy series created by Douglas Adams, debuted as a radio comedy broadcast on BBC Radio 4 in 1978. Since then it has been adapted to other formats, slowly becoming an international multi-media phenomenon over a span of several years. Adaptations have included stage shows, a series of five books first published between 1979 and 1992 (the first of which was titled The Hitchhiker's Guide to the Galaxy), a 1981 TV series, a 1984 computer game, and three series of three-part comic book adaptations of the first three novels published by DC Comics between 1993 and 1996. There were also two series of towels, produced by Beer-Davies, that are considered by some fans to be an "official version" of The Hitchhiker's Guide to the Galaxy, as they include text from the first novel. A Hollywood-funded film version, produced and filmed in the UK, was released in April 2005, and adaptations of the last three books to radio were broadcast from 2004 to 2005. Many of these adaptations, including the novels, the TV series, the computer game, and the earliest drafts of the Hollywood film's screenplay, were all done by Adams himself, and some of the stage shows debuted new material written by Adams.

The title The Hitchhiker's Guide to the Galaxy is often abbreviated as "HHG", "HHGG", "HHGTTG", or "H2G2". The series is also often referred to as "The Hitchhiker's Guide", "Hitchhiker's", or simply "[The] Guide." This title can refer to any of the various incarnations of the story, of which the books, having been translated into more than 30 languages by 2005,[4] are the most widely distributed. The title can also refer to the fictional guidebook The Hitchhiker's Guide to the Galaxy, an eccentric electronic encyclopedia that features in the series. Last but not least, h2g2, launched as the "Earth Edition" of The Guide, is a website now hosted by the BBC featuring a range of user-submitted articles.

Although the various versions follow the same basic plot, they are in many places mutually contradictory, as Adams rewrote the story substantially for each new adaptation. In all versions, the series follows the adventures of Arthur Dent, a hapless Englishman who escapes the demolition of Earth by a bureaucratic alien race called the Vogons with his friend Ford Prefect, an alien from a small planet somewhere in the vicinity of Betelgeuse and researcher for the eponymous guidebook. Zaphod Beeblebrox, Ford's semi-cousin and part-time Galactic President, unknowingly saves the pair from certain death. He brings them aboard his stolen spaceship, the Heart of Gold, whose crew rounds out the main cast of characters: Marvin the Paranoid Android: a manically depressed robot, and Trillian, formerly known as Tricia McMillan, a woman Arthur once met at a party who he soon realises is the only other survivor of Earth's destruction. After this, the characters embark on a quest to find the legendary planet of Magrathea and the Question to the Ultimate Answer.

The first radio series comes from a proposal called 'The Ends of the Earth': six self-contained episodes, all ending with the Earth being destroyed in a different way. While writing the first episode, Adams realised that he needed someone on the planet who was an alien to provide some context, and that this alien needed a reason to be there. Adams finally settled on making the alien a roving researcher for a "wholly remarkable book" named The Hitchhiker's Guide to the Galaxy. As the first radio episode's writing progressed, the Guide became the centre of his story, and he decided to focus the series on it, with the destruction of Earth being the only hold-over.[5]

Adams claimed that the title came from a 1971 incident while he was hitch-hiking around Europe as a young man with a copy of the Hitch-hiker's Guide to Europe book, and while lying drunk in a field in Innsbruck with a copy of the book and looking up at the stars, thought it would be a good idea for someone to write a hitchhiker's guide to the galaxy as well. However, he later claimed that he had told this story so many times that he had forgotten the incident itself, and only remembered himself telling the story. His friends are quoted as saying that Adams mentioned the idea of "hitch-hiking around the galaxy" to them while on holiday in Greece, in 1973.[6]

Adams's fictional Guide is meant to be an electronic guidebook to the Milky Way galaxy, originally published by Megadodo Publications, one of the great publishing houses of Ursa Minor Beta. The narrative of the various versions of the story are frequently punctuated with excerpts from the Guide. The voice of the Guide (Peter Jones in the first two radio series and TV versions, later William Franklyn in the third, fourth and fifth radio series, and Stephen Fry in the movie version), also provides general narration.

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