The book compiles a precise (and often quoted directly from the books concerned) definition of words, lives of historical people, geography of places and events that have appeared in at least one Discworld novel, map, diary, non-fiction book and the short stories "Troll Bridge", "Theatre of Cruelty", and "The Sea and Little Fishes".
The first edition was published in 1994 and listed information from all the novels up to Soul Music, as well as the first two short stories.
The second edition was published in 1997, and adds information up to Maskerade.
The third edition named The New Discworld Companion was published in 2003. It includes articles about books up to Night Watch, as well as Discworld related books and short stories. The book also contains a 10-page interview with Pratchett titled Discworld Quo Vadis?.
All of them also include information that exists on Pratchett's computer, but that he has not yet worked into a novel (for instance, William de Worde is mentioned in the first edition, six years before the publication of The Truth).
At the end of each article is an abbreviation indicating the book(s) in which the word, person, event or place appeared (if there are too many, then no abbreviation is used). The book also includes an introduction by Stephen Briggs and an interview with Terry Pratchett, both of which have also been "updated" in each edition.