Douglas Adams's Guide to The Hitch-Hiker's Guide to the Galaxy is a BBC Radio production sold as an audio book on two cassette tapes (later, two CDs). The programme was partially broadcast by BBC Radio 4 as a 40-minute feature titled The Guide to 20 Years' Hitch-Hiking on 5 March 1998, marking the 20th anniversary of the first radio programme in the Hitchhiker's Guide to the Galaxy series. Source: Wikipedia (en)