‘THE MABINOGION’ is a collection of eleven Welsh prose tales culled from the Red Book of Hergest – a manuscript copied-out in about 1400. The collection was given its name by Lady Charlotte Guest, who published the first English translations between 1838 and 1849.
The eleven tales fall into three groups:
  1. ‘The Four Branches of the Mabinogi’ – a group of four related mythological stories: ‘Pwyll Prince of Dyfed’, ‘Branwen Daughter of Llŷr’, ‘Manawydan Son of Llŷr’ and ‘Math Son of Mathonwy’.*
  2. Four independent tales from Welsh tradition: ‘The Dream of Macsen Wledig’, ‘Lludd and Llefelys’, ‘Culhwch and Olwen’ and ‘The Dream of Rhonabwy’ – the latter two of which feature King Arthur.
  3. ‘The Three Romances’ – three Arthurian stories that show French influence: ‘The Lady of the Fountain’, ‘Gereint Son of Erbin’ and ‘Peredur Son of Efrawg’.
A slightly earlier manuscript, the White Book of Rhydderch of about 1350, contains most of ‘The Mabinogion’ – ‘The Dream of Rhonabwy’ is missing.* Other manuscripts contain individual tales from the collection, or fragments of them, copied-out during the hundred-or-so years before the White Book.
The Red Book of Hergest (Llyfr Coch Hergest) is named from its red leather binding and, its former home, Hergest Court in Herefordshire. It is now in the Bodleian Library, Oxford (Jesus College MS 111).
The White Book of Rhydderch (Llyfr Gwyn Rhydderch) was probably written-up for one Rhydderch ab Ieuan Llwyd, from Parcrhydderch, Ceredigion. Originally it was a single volume, presumably with a white binding at some stage, but it is now in two volumes, Peniarth MS 4 (which contains ‘The Mabinogion’ stories) and Peniarth MS 5, in the possession of the National Library of Wales.
At the end of each of the ‘Four Branches’ is a statement to the effect: ‘with that, this branch of the mabinogi ends’.  In the case of ‘Pwyll’, instead of mabinogi, the word mabinogion (spelled mabynnogyon in the manuscript) is used. Lady Charlotte thought this was the plural of mabinogi, and borrowed the word as her title for the whole collection. There is now a general consensus, however, that mabynnogyon was originally a scribal error, and that it should really have been mabinogi, as in the other ‘Branches’. Nevertheless, “The Mabinogion” remains a convenient collective name for the eleven tales. Incidentally, the meaning of mabinogi is not clear – it is presumably derived from mab = ‘boy’ or ‘son’.
‘Lludd and Llefelys’ and ‘Culhwch and Olwen’ survive only as fragments in the White Book. There is, however, no evidence to support the notion that it did originally contain ‘The Dream of Rhonabwy’. The word mabynnogyon is found in the same relative position in the White Book as it is in the Red Book. Possibly, the Red Book used the White Book as a source, or they each used a common, no longer extant, antecedent.