The Hitchhiker's Guide to the Galaxy (1979, ISBN 0330258648) is the title of the first of five books in the Hitchhiker's Guide to the Galaxy comedy science fiction series by Douglas Adams. The novel is an adaptation of the first four parts of Adams's radio series of the same name.

Note: The title The Hitchhiker's Guide to the Galaxy is often abbreviated as "HHG", "HHGG", "HHGTTG" or "H2G2". Unfortunately, the different editions of the Hitchhiker's Guide spell it differently -- so you'll find "Hitch-Hiker's Guide", "Hitch Hiker's Guide" as well as "Hitchhiker's Guide" in different editions (US or UK), versions (audio or text) and compilations of the book. For the sake of coherence Wikipedia spells it Hitchhiker, which is reportedly the way Adams himself preferred it.

The novel takes its name from the fictional book The Hitchhiker's Guide to the Galaxy, a fictional guidebook written in the form of an encyclopedia.

The Hitchhiker's Guide to the Galaxy ('The Guide is definitive; reality is frequently inaccurate') is the most popular known reference work for two reasons: it is inexpensive, and it has the words 'Don't Panic' written on it in large, friendly letters. It is a galactic bestseller everywhere except on that backward planet Earth, where they still think digital watches are "A pretty neat idea". One morning, to the disappointment of few, the entire planet is demolished to make way for a "hyperspace bypass". However, one of the supposed Earthlings is actually Ford Prefect, a Betelgeusian roving reporter for the Guide, and just before the planet goes bust he hitches a ride on one of the destroying craft, dragging along his permanently baffled Earthling friend, Arthur Dent. The two narrowly escape death in deep space through the mysterious workings of the Infinite Improbability Drive, which powers the starship Heart of Gold. Unfortunately, the starship Heart of Gold has just been stolen by Ford's semicousin Zaphod Beeblebrox, former president of the Galaxy, and his girlfriend Trillian. It is only when the band stumbles upon the legendary planet of Magrathea that Trillian learns that the pet mice she brought with her are in truth hyper-intelligent pan-dimensional beings, seeking the question to the ultimate answer of Life, the Universe, and Everything.