By most accounts the pre-christian Celts practiced a polytheistic religion from about 500 BCE to 500 CE. Celtic tradition and stories are full of gods and goddesses. However, the Celtic pantheon was/is unlike in Goddesses and Gods in Greece and Rome who, for the most part, had clear functions. Jupiter was the King of the Gods, and Juno was the Queen, Neptune was the God of the Sea, Mars was the God of War, and Venus was the Goddess of Love.
In the Celtic tradition the same clarity doesn't exist and not only that, the deities change from one Celtic group to another. The Gaulish (France, Southwest Germany, Netherlands, Holland, Luxembourg, and Northern Italy) and Brythonic (Great Britain and Brittany) deities differ from the Welsh (Wales) deities, who differ from the Gaelic (Ireland and Scotland) deities, who differ from the Celtiberian (Portugal and Spain) deities. In addition to the Big Pantheon, it appears that each tribe or tuath had its own local deity. This is reflected in the oath found in early Irish literature, "I swear by the gods my people swear by."
To keep this post simple I'm going to focus on my Top Ten Celtic Deities that seem to appear in most of the Celtic groups in one form or another. Obviously you may have others in your top ten list because the identification with deity is highly personal. Here are mine in alphabetical order:
To learn more about the Celtic Goddess and Gods I recommend the book, The Isle of the Many Gods: An A-Z of the Pagan Gods & Goddess Worshipped in Ancient Britain During the First Millenium CE Through to the Middle Ages by Rankine and D'Este. The title is rather ponderous but its one of the better books about the Celtic Gods. If you want to dive deeper into the lore of horned gods then Horns of Power: Manifestations of the Horned God by D'Este, Rankine and Huggens is quite good.
May you find peace on your path,
I'm Dr. Dave, a modern druid. I lived and worked in Bolivia and Peru for over six years, where I and was trained by Andean Shamans, and today practice Druidcraft and contemporary shamanism.