This book has been several years in the making, and it is at last my pleasure to be able to acknowledge the assistance I have received from many people. The volume owes its origin to a doctoral thesis submitted to the University of St Andrews, and my debt to my supervisor, Professor D. E. R. Watt, is deep. His incisive comments saved me from many errors and inconsistencies, and among many kindnesses he generously loaned me his own microfilm copy of the account of the Scottish collector William de Grenlaw. I am most grateful also to Mr J. J. Robertson of the University of Dundee, who helped me with the chapter on papal justice.

Historians are always indebted to the specialist services provided in archives and in academic libraries, and my work was much eased by the courtesy of the staff of St Andrews University Library, especially Miss S. Rowe, the Inter-Library Loans Librarian, and the staff of the Department of Manuscripts and Rare Books, Mr G. D. Hargreaves, Mr R. N. Smart and Mrs Christine Gascoigne. Their willingness to respond to what must sometimes have seemed strange requests and their readiness to grant me immediate access to a number of microfilms and rare books greatly facilitated the research on which this volume is based. I am also most grateful to the staff of the Minster Library in York, especially the Archivist, Mr M. S. Dorrington, for his advice and kindness in providing manuscripts at short notice.