Life, the Universe and Everything (1982, ISBN 0345391829) is the third book in the five-volume Hitchhiker's Guide to the Galaxy science fiction trilogy by Douglas Adams. The title refers to the Answer to Life, the Universe, and Everything.

The story was originally written by Adams as a possible film outing for the Doctor Who television series (with Tom Baker as the Doctor), although it was never produced.

A radio adaptation of Life, the Universe and Everything was recorded in 2003 under the guidance of Dirk Maggs, starring the surviving members of the cast of the original Hitchhiker's radio series. Adams himself, at his own suggestion, makes a cameo appearance; due to his death before production began on the series, this was achieved by sampling his character's dialogue from an audio book of the novel read by Adams that was published in the 1990s. The radio adaptation is to debut on BBC Radio 4 in September 2004.

This book is the only in the Hitchhiker's Guide to the Galaxy series to have been censored in its U.S. edition. An extensive but still incomplete list of the changes between the two versions can be found on an archived web page (http://web.archive.org/web/20030214214643/http://www-personal.umd.umich.edu/~nhughes/dna/faqs/diff.html) (warning: contains spoilers).

Having decided to enjoy being stranded on pre-historic Earth by going insane, the hapless Arthur Dent is sidetracked by the sudden reappearance of Ford Prefect, who pulls him through an eddy in the space-time continuum and into Lord's cricket ground in the 1980s. Unfortunately, the pitch is about to be the scene of a shocking act of intergalactic terrorism. Slartibartfast, former designer of fjords, has set out in a ship powered by the awe-inspiring Bistromathic drive to try to prevent an ancient evil from destroying the universe. The reader also gets to find out about the bowl of petunias.

The novel is the last in the series to feature the characters of Zaphod Beeblebrox and Slartibartfast.