Collective religious enthusiasm was a surprisingly many-sided, influential and widespread phenomenon in medieval Europe. Amongst the forms it took were remarkable revivalist movements like the flagellants of 1260; popular crusades like the often mythologized ’children’s crusade’ of 1212 and the 'shepherds' crusade’ of 1251; as well as popular excitement involving living saints and their veneration (115 cults in Perugia). This book focuses upon particular thirteenth-century revivals and popular crusades, but does so in order to illuminate the nature of medieval western religious enthusiasm by exploring such topics as crowds, penitential self-laceration, charismatic leaders, prophecy, runaway youths, popular crusading fervour, dreams, and sanctity, male and female. A previously unpublished essay introduces the book, initiating a discussion of religious enthusiasm in the medieval West and the second conversion of Europe.