The long lost, original Latin text for Vita Griffini Filii Conani is shown with an English translation in this critical edition. The main focus of this volume is on the Welsh and Latin version of Peniarth MS, 434E, which has been heavily annotated and corrected to show that what had been thought to be the only dependable source had not in fact been an accurate translation. This discovery not only impacts medieval Welsh historians but also those involved in the translation of medieval works.