This book was first published in 1980. Walter Ullmann made substantial contributions to many areas of medieval studies, and to those of papal history and cannon law particularly, which have been distinguished by quality and quantity alike. The bibliography of his published work included in this volume contains almost four hundred items. No less influential for generations of students have been his teaching and lecturing, especially at Leeds and from 1949 to 1978 at Cambridge. In Authority and Power friends and former pupils combined to mark his retirement from the Cambridge Chair of Medieval History, with each contributor writing on or near the subject originally studied under Professor Ullmann's supervision. The essays serve both to acknowledge a sense of shared indebtedness to Professor Ullmann and to indicate new approaches and developments, as they were at the time, in legal-historical scholarship.