My interest in the history of medieval treason dates back ten years or more and sprang, I believe, from my early postgraduate training under Professor J. S. Roskell. I began serious investigation in 1961 and continued thereafter whenever the exigencies of teaching and academic administration allowed. Much of the present book was offered as a thesis for the degree of Ph.D. of the University of Nottingham. This work was supervised by Dr R. L. Storey, who gladly undertook the task of guidance in a field that was at first unfamiliar to him and did so in a manner which was encouraging, stimulating and most effective. His deep knowledge of the Public Records was an immense boon and his criticism, ever friendly, not less so.

My gratitude is also extended to Professor S. F. C. Milsom, whose valuable advice has saved me from more than one serious error, to the General Editor of this Series, Mr D. E. C. Yale, who pointed out certain omissions, and to my wife, for her continuous encouragement.

Although I have felt it necessary to go back as far as the laws of classical Rome by way of introduction, this book is concerned in essence with the period from the middle of the thirteenth century to the end of the fifteenth, the prelude to the great treason statute of 1352 and the aftermath. I feel no obligation to justify the importance of the theme. No one studying the constitutional, the legal, or the political history of later medieval England can fail to be impressed by the vital role of treason in the development of concepts and institutions in this period.