So Long, and Thanks for All the Fish is the fourth book of the Hitchhiker's Guide to the Galaxy "trilogy of six books" written by Douglas Adams. Its title is the message left by the dolphins when they departed Planet Earth just before it was demolished to make way for a hyperspace bypass, as described in The Hitchhiker's Guide to the Galaxy. A song of the same name was featured in the 2005 film adaptation of The Hitchhiker's Guide to the Galaxy.

The Hitchhiker's Guide to the Galaxy is the first book in the Hitchhiker's Guide to the Galaxy comedy science fiction "trilogy of five books" by Douglas Adams, with a sixth book written by Eoin Colfer. The novel is an adaptation of the first four parts of Adams's radio series of the same name, centering on the adventures of the only man to survive the destruction of Earth; while roaming outer space, he comes to learn the truth behind Earth's existence. The novel was first published in London on 12 October 1979. It sold 250,000 copies in the first three months.