This survey presents the mythic and legendary traditions of Gaelic and British Celts, outlining sources and the religion of the ancient Britons, including druidic elements. It summarizes the principal cycles: the arrival and deeds of the Gaelic gods, sun-god motifs, voyages and wars with giants, the Ulster heroic epic, Finn and the Fenians, and love-stories; then the British gods, adventures in the otherworld, the Branwen episode, enchantments, victories of light, and the mythic coming of Arthur, showing how deities transform into knights and later fairies. It concludes by tracing survivals of Celtic paganism into later folklore and offering notes and bibliography for further study.