The initial impetus for this book arose from our preparatory work for the Welsh edition of "Culhwch ac Olwen", which we undertook in 1985 at the invitation of the Language and Literature Committee of the Board of Celtic Studies, and which was published in 1988 by the University of Wales Press under the title "Culhwch ac Olwen: Testun Syr Idris Foster wedi ei olygu a’i orffen gan Rachel Bromwich a D. Simon Evans". Our commitment as editors of the preparatory material for an edition of this tale, which was left unfinished by the late Sir Idris Foster at his death, allowed us to add little to a work whose main purpose was to make the text of "Culhwch ac Olwen" available with the minimum of delay for study by students in the University of Wales. This restriction prevented us from offering the full critical apparatus and discussion which we had prepared in readiness, and which was plainly required by the central importance of "Culhwch ac Olwen" for all students of medieval Welsh literature. We therefore welcomed the opportunity to prepare this extended study, to which we have supplied a full glossary, a revised edition of the notes already assembled for the Welsh edition, and a newly-written introduction. The text of the tale here printed corresponds line-by-line with that of the Welsh edition, with the exception only that we have substituted English subtitles for those which we supplied previously in Welsh, and we have made a few minor corrections to the text. We hope that this English edition of "Culhwch ac Olwen" may reach a wider readership among students and scholars than has its predecessor. (Preface)