In its original version, this study of canonical practice was presented as a Ph.D. thesis at the University of California, Berkeley. I know that it retains, after two revisions, many faults. But it would be a worse book than it is without the help of several people, and I want to express my appreciation to them publicly. Professor John T. Noonan, Jr first interested me in the subject of the history of marriage law. My work owes much to his continued thoughtful guidance and criticism. Professors Peter Herde and Robert Brentano also guided me in the early stages of my work in canon law, and their advice and encouragement I have valued greatly. Mr G. D. G. Hall was kind enough to read the entire text, parts of it more than once. His excellent and penetrating criticism has greatly improved the final product. Professors Charles Donahue and Peter Riesenberg also read through earlier versions of the work, making many helpful suggestions which I have incorporated in the text.

I want also to thank the Keeper of Manuscripts and the Archivist of the Library of the Dean and Chapter, Canterbury, successively Dr William Urry and Miss Anne Oakley, and the Director of the Borthwick Institute of Historical Research in York, Mrs N. K. M. Gurney, for permission to reproduce substantial portions of the MSS. in their care. I am very grateful for the help which they, and the many other archivists I have troubled with queries about documents, unfailingly offered to me.