Welsh mythological prose finds its most enchanting breath in the Mabinogion, a collection of stories about the gods and goddesses of the Celtic Britons. More formally the work is known as the Four Branches of the Mabinogi. Although the full set of tales cannot be told here, an introduction of the Briton deities will be made within the specific branch they play a role in.

• Branch One of the Mabinogi--Pwyll, the Prince of Dyfed in southern Wales, works a bargain with Arawn, ruler of the Underworld, whereby Pwyll governs there for a period and eventually becomes the Pen Annwn (or Head of the Underworld). Pwyll then woos for his wife Rhiannon, the daughter of Heveydd the Ancient. To win her, Pwyll outwits the suitor Gwawl with the help of a magic bag. Pwyll and Rhiannon marry and have a son named Pryderi, who plays major roles in other Mabinogion tales.
• Branch Two of the Mabinogi--Brân the Blessed and his sister Branwen the Fair Bosomed are principals in a both tragic and comic tale where the forces of Wales are pitted against their Celtic counterparts in Ireland. Branwen marries the king of Ireland and they have a son named Gwern. Upon the treacherous death of her son, Branwen dies of a broken heart. The Welsh seek vengeance and battle furiously against the Irish. Brân is struck down, but continues to bring good humor among his band of warriors. More on Brân is given below.
• Branch Three of the Mabinogi--Pryderi gives the realm of Dyfed to Manawyddan, the sole surviving child of Llyr. By this time Pwyll has somehow disappeared from the mythic scene, and Pryderi offers his mother Rhiannon as a wife to Manawyddan, thus further calming the latter's sorrows. Manawyddan and Rhiannon, and Pryderi and his wife Kieva all become close companions in the adventures ahead. But the dilemma is that someone is casting enormous spells on Dyfed, turning it from a rich territory to a wasteland. And castles appear out of nowhere, then vanish with loved ones trapped inside. Vengeance is the source of the riddle, though Manawyddan, Pryderi, and their wives end the tale with happy sentiments.
• Branch Four of the Mabinogi--Gwydion and Arianrod, being children of the goddess Dôn, were high in the Briton pantheon. Gwydion was a sort of druid of the Welsh gods, a "master of illusion and phantasy." He was a friend and helper of mankind, and a constant fighter against the powers of the underworld, the realm of Annwn. Arianrod, called the "Silver Circle," bore two sons--Dylan and Lleu. Dylan had a great affinity for the sea, and swam as well as the best fish in the ocean. It is said that the waves of Britain wept for Dylan at his death. Arianrod had poor bonds with her other son Lleu, and his care was left largely to Gwydion. Mâth, the brother of the goddess Dôn, was a master of magic and Gwydion's teacher of spells.