From the back cover of the core book
Open ended, world-building adventure was the only kind of tabletop role play gaming at the time it was introduced in 1974. The rules for those "sandbox" campaigns lie scattered, primarily across three little paperback booklets, full of obscure stats, unexplained tables, and vague references to other rule sets - not included!
Champions of ZED puts it all together, clearly, and under one cover, along with notes from long lost drafts, and house-rules from the games' two original designers. At last, enjoy the endless possibilities of Zero Edition Dungeoneering!