Ecclesiastical Knights is a spirituality study of the three military orders of Santiago, Calatrava, and Alcántara in León-Castile from the twelfth to the early fourteenth centuries. It explores the fundamental problem of the military orders: how the seemingly incongruous traditions of knighthood and monasticism were combined into a single way of life. Ecclesiastical Knights rejects the term “warrior monks” as inaccurate and misleading, and proposes the alternative “ecclesiastical knighthood.” According to this model, the military brethren sought to consecrate the exercise of arms in service of the Church by taking religious vows and appropriating those aspects of the monastic tradition that served their mission. While the Templars were the pioneers of this way of life, pious knights in Iberia followed their example, responding to local circumstances and needs, and taking advantage of the support of civil and ecclesiastical powers, to form their own communities. Ecclesiastical Knights offers three perspectives on how the Iberian orders lived: from the standpoint of their internal organization, devotion, and discipline; from the standpoint of their mission to fight, care for the sick, and ransom captives; and from the standpoint of their relations with one another and the friendships they sought to establish through formal pacts of cooperation. The evidence reveals communities of men and women for whom the exercise of charity was the coordinating ideal behind their various activities, and who made a crucial contribution to the ultimate success of Reconquest and crusade in Iberia. Their hybrid way of life made the military orders the greatest of those who fought, and the least of those who prayed, in the European Middle Ages.