"A grand and important book not only for those bitten by medieval studies but for all interested in Western civilization's transition from medieval to modern." (American Historical Review) "A wonderfully rich and rewarding book. . . . This work will, unquestionably, remain the standard work for years to come." (Speculum) "This is a painstakingly detailed narrative into which analysis is seamlessly woven. . . . A major contribution on several fronts." (Church History) "This will be the definitive study of a noteworthy religious movement of the later Middle Ages. Van Engen has mined the libraries and archives with extraordinary thoroughness and has found a wealth of new knowledge." (Robert E. Lerner, Northwestern University)