The books are described as "a trilogy in five parts", after having been described as a trilogy on the release of the third book, and then a "trilogy in four parts" on the release of the fourth book. They have a wide following around the world, thanks to their outlandish situations, characters and concepts (eg. Babel fish, Vogon poetry, Slartibartfast and other minor characters, The Answer to Life, the Universe, and Everything), their anarchic, ironic humour, and their subtle social commentary.
The series was originally going to be called 'The Ends of the Earth' and each episode would end with the Earth being destroyed in a different way each week but this idea was scrapped and the Hitchhiker's Guide was born.Hitchhiker's Guide spell it differently -- thus "Hitch-Hiker's Guide", "Hitch Hiker's Guide" and "Hitchhiker's Guide" are used in different editions (US or UK), versions (audio or text) and compilations of the book. For the sake of coherence, Wikipedia spells it Hitchhiker's Guide, which is reportedly the way author Adams himself preferred it.