This book was researched and written during my tenure of a British Academy Research Readership between October 2002 and September 2004. My first and greatest debt is to the British Academy for making it possible to immerse myself in the complexities of the twelfth century free from the routine distractions of university life. I am equally indebted to my colleagues in the History of Art Department of the University of York for making it possible for me to take leave of absence from the usual obligations of teaching and administration during this period.

Special thanks are due to the staff of York Minster Library, particularly Mrs Deirdre Mortimer and Mr John Powell, who, together with the Minster Archivist, Mr Peter Young, provided a service of unfailing courtesy and efficiency, even during circumstances of the greatest difficulty. The excellent resources of the Minster Library and Archives provided convenient access to most of the materials required for the research. Additional resources were provided by the University of York Library, to whose staff I am equally indebted.

I have benefited enormously over the years from discussions with and help from many colleagues at the Centre for Medieval Studies at the University of York. In particular, Dr Sarah Rees Jones, Professor David Smith, Dr James Binns and Chris Daniell have assisted on a number of points of detail, and Mrs Louise Harrison has provided unfailing and ever-cheerful service on the word-processor. Professor David Palliser has also advised on a number of issues. My scholarly debt to previous labourers in the field of twelfth-century ecclesiastical history will be apparent on every page that follows. Any tares that remain are my own responsibility.

This project was originally undertaken as essential background research for a study of the early fifteenth-century stained glass window in York Minster illustrating the life and miracles of St William of York. It rapidly became apparent, however, that much of the historical spadework on William fitzHerbert and such key sources as the Vita of St William had yet to be done, and that it required far more extensive treatment than could possibly be fitted into a preliminary chapter in a book on the St William Window. The result will, I hope, stand on its own merits.