The Llywelyn ab Iorwerth genealogies were in many ways the culmination of the medieval Welsh genealogical tradition. This collection was the longest genealogical text ever produced in medieval Wales. It drew on a large number of pre-existing written sources, including many earlier genealogical texts, and also incorporated a substantial amount of original material. Perhaps most significantly, it exercised an enormous influence on the burgeoning Welsh genealogical tradition of the fifteenth to eighteenth centuries, becoming, in its proliferating number of versions, almost the sole source of early modern knowledge about medieval Welsh genealogy.

Despite its considerable importance, Peter Bartrum is the only scholar previously to have granted this text any sustained attention. Bartrum recognised that a large proportion of the text as found in its fifteenth- to eighteenth-century manuscripts dates from the thirteenth century, and he realised the value of placing its contents at the disposal of modern scholars. But less attention was given to the status of the material as a cohesive textual product, with a date and place of composition, an organised internal structure and raison d’être. Consequently, Bartrum felt at liberty to rearrange the text as he saw fit, group together sections of different recensions that came into being at different times, and divide the text into four separate editions, to which he gave the titles ‘Plant Brychan’, ‘Bonedd yr Arwyr’, ‘Achau Brenhinoedd a Thywysogion Cymru’ and ‘Hen Lwythau Gwynedd a’r Mars’. Only the first of these titles is present in the manuscripts. The result was a mélange of portions of text composed between the thirteenth and sixteenth centuries, granting scholars access to a significant amount of genealogical information whilst obscuring completely the various contexts to which that information properly pertained.

A different approach has been taken during the production of the editions appearing in Appendix B of this book. The overriding concern has been to treat the Llywelyn ab Iorwerth genealogies and their derivative recensions as texts rather than as miscellaneous repositories of genealogical exposition. All aspects of the texts have been treated as of equal value: not only names and relationships, but also structure, phraseology and orthography. In the first instance, textual accuracy has been treated as more important than genealogical accuracy.