Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Mostly Harmless is a novel by Douglas Adams and the fifth book in the Hitchhiker's Guide to the Galaxy series. It is described on the cover of the first editions as "The fifth book in the increasingly inaccurately named Hitchhikers Trilogy."The title derives from a joke early in the series, when Arthur Dent discovers that the entry for Earth in The Hitchhiker's Guide to the Galaxy consists, in its entirety, of the word "Harmless." His friend Ford Prefect, a contributor to the Guide, assures him that the next edition will contain the article on Earth that Ford has spent the last 15 years researching-somewhat cut due to space restrictions, but still an improvement. The revised article, he eventually admits, will simply read "Mostly harmless.