The monastery of Walden was founded c.1136 by Geoffrey de Mandeville, a prominent baron in the civil war of Stephen's reign. Its site just outside the town of Saffron Walden in Essex is now occupied by the great Jacobean mansion known as Audley End House. The Book of the Foundation of WaldenMonastery, written by a Walden monk soon after 1203, is here printed in its entirety for the first time. This lively narrative relates the history of the Mandeville earls of Essex and the inheritance of their lands and title by King John's justiciar, Geoffrey fitz Peter. The monk-author describesthe development of the priory at Walden and its elevation to the status of a Benedictine abbey in 1190, and in the final section of the work he traces the consequent conflict with Geoffrey fitz Peter, concluding the story with the death of Abbot Reginald in 1200 or 1203. The interest of The Book ofthe Foundation of Walden Monastery extends far beyond the local: the editors' introduction and notes establish its position as a valuable historical source.