First published in 1934, this volume explores the varied roles of bishops alongside monks, administrators, magnates and scholars in the reforms surrounding the Lateran Council of 1215 and the Council of Trent, with a particular focus on approaches to their implementation in England. The book was originally written in the form of two theses published in 1931 under the titles of 'The Episcopate during the Reign of Henry III' by Marion Gibbs and 'The Enforcement of the Decrees of the Lateran Council of 1215 in England during the Reign of Henry III' by Jane Lang. They have been made into one volume here, with the first two parts by Marion Gibbs and the third by Jane Lang.