In the concluding stages of the eleventh century Eucharistic controversy, which turned on whether, and how, sacramental consecration changed the nature of bread and wine at the altar, Alberic of Monte Cassino composed a small but important manuscript. Alberic was the most renowned teacher of his age, and his treatise, buttressed by appeal to the authority of the Church Fathers, was said by contemporaries to have ''utterly destroyed'' the arguments of his opponent, Berengar of Tours, who held that the bread and wine did not change materially into the body and blood of Christ. Unfortunately, modern scholars had long believed this crucial document lost. This book, which includes the full Latin text and translation of this manuscript, demonstrates that Alberic's treatise, far from being lost, is a text that can be identified and has been known to scholars for years. By showing conclusively that this text was in fact written by Alberic, Radding and Newton transform our understanding not only of the particulars of the controversy and papal politics, but also of the intellectual process by which theological truths took shape in medieval Church councils.