John Cassian is a study of the fifth-century monk who was one of the founders of western monasticism. Christian monasticism flowered in Egypt during the fourth century. Cassias spent several years in Egypt and his writings are important evidence of the earliest period of monastic life. Later in life Cassian came to Provence and adapted the Egyptian ideals and methods for Latin use. The Benedictine Rule owes much to his influence. Benedictine monks still look back upon Cassian as an authority for their way of life. He was the first guide to the contemplative ideal in the history of western thought. Cassias questioned the doctrine of predestination taught by Augustine. Dr Chadwick shows how this argument gave him an ambiguous reputation in medieval history. The first edition of this book was published in 1950. It established itself as a contribution to the history of monasticism and to the origins of the contemplative ideal in Christianity. This is a reprint of the 1968 second edition in which Dr Chadwick made changes to take account of important work published since the first edition.