The Hitchhiker's Guide to the Galaxy is a five-book trilogy

The Hitchhiker's Guide to the Galaxy is a literary series forming a pentalogy that the author Douglas Adams humorously nicknamed a trilogy in five parts. These novels were written between 1979 and 1992 based on loose adaptations of the initial radio serial. The work was then extended in 2009 with the publication of a sixth volume written by Eoin Colfer.