Llyfr Gwyn Rhydderch (the White Book of Rhydderch) is one of the most notable and celebrated manuscripts in the National Library of Wales. It is the earliest compendium of Welsh prose texts, though it also contains some examples of early Welsh poetry. Today what was one manuscript is divided into two volumes. In Peniarth MS 4 (seen here) we find the earliest copy of those Middle Welsh tales now collectively known as the Mabinogion: 'The Four Branches of the Mabinogi', 'Culhwch and Olwen', 'The Dream of Macsen Wledig', 'Lludd and Llefelys', 'Peredur', 'Owain' (also known as 'The Lady of the Fountain'), and 'Geraint and Enid'. There is no evidence to suggest that it ever contained 'The Dream of Rhonabwy', which is included in Llyfr Coch Hergest (the Red Book of Hergest, copied between 1382 and c. 1400, now MS Jesus College 111, in the Bodleian Library, Oxford). Peniarth MS 5 contains religious prose and adaptations into Welsh of tales from other languages.
The White Book was copied in the mid-fourteenth century, most probably for Rhydderch ab Ieuan Llwyd (c. 1325-1400) from Parcrhydderch in the parish of Llangeitho in Ceredigion. Rhydderch, who came from a family with a long tradition of literary patronage, held posts under the English Crown but was also an authority on native Welsh Law. The hands of five scribes have been identified in the manuscripts, very likely working in Strata Florida abbey, not far from Rhydderch's home. It is possible that he also owned the Hendregadredd Manuscript.
The manuscript's name can be assumed to refer to the colour of an early binding, and to its first owner. In its original form the volume would have been larger and thus more imposing, but when it was rebound in the early modern period the leaves were cropped, affecting their appearance.
After Rhydderch's death the manuscript seems to have remained in the family's possession until about the middle of the fifteenth century. By then the White Book was in Rhiwedog, near Bala. Antiquaries and scholars in north-east Wales realised its significance, as witness the transcripts they made from it: Richard Langford of Trefalun in 1573, Roger Morris (fl. 1580-1607) from Coedytalwrn, Sir Thomas Wiliems, in about 1594, and Jasper Gryffyth (d. 1614). By about 1634 the manuscript was in the hands of the famous Flintshire antiquary and copyist, John Jones of Gellilyfdy. Some time after 1634 the pioneering lexicographer Dr John Davies of Mallwyd made a list of its contents, which reveals that some of its leaves had already been lost. When John Jones died, about 1658, the manuscript, which had already been divided into two volumes, was acquired by Robert Vaughan and incorporated in his famous library at Hengwrt in Merionethshire. In 1859 the Hengwrt collection, including the White Book of Rhydderch, was transferred to Peniarth by its new owner, W. W. E. Wynne. In 1904 it was bought by Sir John Williams who presented it to the National Library as one of its founding collections. In 1940 the White Book was rebound in goatskin by Carl Hanson, the head of the Library's bindery.