The Four Branches are the core and the only tales the medieval text itself groups together. Pwyll tells of the prince of Dyfed who exchanges places with a lord of the otherworld, wins Rhiannon, and loses and recovers their son Pryderi. Branwen turns on the marriage of Branwen to the king of Ireland, her humiliation, and a catastrophic war in which the giant Bran is mortally wounded and his severed head continues talking to his companions for eighty years. Manawydan is a strange, quiet tale of enchantment and an emptied land, resolved by a bargain over a pregnant mouse. Math contains the making of a woman out of flowers, her transformation into an owl, and the magician Gwydion and his nephew Lleu.
The native tales are separate compositions. Culhwch and Olwen is the earliest Arthurian prose tale in any language, probably late eleventh century, and pairs an enormous catalogue of Arthur's warriors with a sequence of impossible tasks. The Dream of Rhonabwy is a sardonic dream-vision, the Dream of Macsen Wledig attaches a Welsh legend to a Roman emperor, and Lludd and Llefelys explains three plagues on Britain.
The three romances, Owain, Peredur and Geraint, correspond closely to Chretien de Troyes' Yvain, Perceval and Erec. The relationship is much argued: whether the Welsh versions derive from Chretien, whether Chretien and the Welsh drew independently on shared Breton or Welsh material, or some combination. No settled answer exists, and the tales differ from the French in ways that do not look like straightforward translation.