The tales create a dreamlike atmosphere and preserve much of the primitive, fascinating world of Celtic myth. They exemplify the heroic and idealistic world of Celtic literature. The Mabinogion does not seem to have been very well known until its translation into English in 1849 when Lady Charlotte Guest's version appeared. The tales comprise an ensemble of parts, the first four "Pwyll", "Branwen", "Manawydan", and "Math" comprising the Four Branches of the Mabinogi. It was Lady Charlotte who supplied the title Mabinogion. Previously, the tales were simply identified as part of this or that manuscript. Each of the Four Branches ends with the term 'So ends this Branch of the Mabinogi.' The Welsh word 'mab' means 'son'. Lady Charlotte concluded that 'mabinogi' was a noun meaning 'a story for children' and that the word 'mabinogion' was its plural. Another interpretation is that the word mabinog refers to "a student in the bardic class" and mabinogi (pl. mabinogion) therefore being "a tale belonging to the mabinog's repertoire".

The Mabinogion are found in the "Red Book of Hergest", a large fourteenth-century manuscript kept at Jesus College, Oxford. An earlier manuscript called 'The White Book of Rhydderch' (c. 1325) is incomplete but more than likely contained all the tales when it was whole. Fragments of these tales appear elsewhere, the earliest of which is believed to be 'Peniarth 6' which dates to c. 1225. The stories were probably drawn up in their present shape towards the end of the twelfth century, but the stories are of much greater antiquity, some belonging even to the more distant past of Celtic paganism and to the period of Gallo-Breton unity. Welsh scholars tend to favour an earlier amalgamation, wanting to maximize the extent of their ancestors' contribution to The Mabinogion, while French scholars argue for 1200 - 1250 CE with the same thing in mind. Ifor Williams proposed 1060 CE as a likely date and gives a number of arguments: the occurrence of outdated word forms in the text, the scarcity of French words, references to extinct customs, and the peaceful period 1055-63 which was a time of bards from north and south to exchange and tell their tales.

It is interesting to note that in the main "Four Branches" there is no mention of Arthur. Besides these four tales, the Mabinogion includes two from romantic British history ("The Dream of Maxen Wledig" and "Lludd and Llevelys"), two more interesting ones ("Rhonabwy's Dream" and "Kilhwch and Olwen"), "Taliesin", and, finally, three tales ("Owain or The Lady of the Fountain", "Gereint the Son of Erbin", "Peredur ab Evrawc") which show a marked kinship with certain medieval French tales.

The three-volume edition with English translation by Lady Charlotte Guest was printed by Llandovery in 1849 with the English translation alone appearing in an edition of 1879. The Welsh text has been printed in a diplomatic edition, "The Red Book of Hergest", by J. Rhys and J. Gwenogfryn Evans (Oxford, 1887). Lady Guest's translation has been re-edited with valuable notes by Alfred Nutt (London, 1902).