During the several years when I researched Gratian's Decretum, I incurred a number of scholarly and personal debts, which I am happy to acknowledge. In the first place, I want to thank my mentor, Robert Somerville, who supervised my dissertation at Columbia University and who continues to take great interest in my work. He has read the entire book in manuscript. His advice, support, and personal kindness over the years were and are invaluable and deeply appreciated. I owe him special thanks for putting his collection of microfilms of pre-Gratian canonical manuscripts at my disposal.

Rudolf Weigand of the University of Würzburg generously shared his enormous knowledge of the Decretum and the decretists, served on my dissertation committee, and continued to be a greatly valued discussion partner until shortly before his untimely death. I am particularly grateful to him for allowing me to use his large collection of microfilms of Decretum manuscripts. I am saddened that my thanks can no longer reach him.

Several fellow scholars very kindly put their unpublished materials at my disposal, and I want to thank them for their great generosity, and especially Martin Brett, Horst Fuhrmann, and Peter Landau. Many friends, colleagues, and teachers (most of whom would fit all three categories) helped me with intelligent criticism, valued information, stylistic advice, and encouragement.