Celtic Lunar Astrology is essentially a Druid Zodiac. The Druids were a sect of Celtic priests who inhabited the British Isles around 1000 B.C. The Druids used a lunar calendar consisting of 13 months, each being 28 days long, plus one intercalary day. The Druid religion was based mainly upon an awareness of natural and supernatural energies. These energies were identified with spirits or dryads who dwelt within the ancient trees. Druids believed that trees were given spirits and attributes from the Sun, which was perceived as a symbol of the Supreme Being. Thus, trees were considered living entities, possessed with Infinite Knowledge and Wisdom...symbolically representative of the Cyle of Life, Death and Renewal.

The Celts envisioned the entire Universe in the form of a tree, whose roots grew deep into the ground and whose branches reached high into the Heavens. In time, the Celtic people eventually designated a tree to each Moon Phase in their calendar in accordance with its magical properties. Therefore, the Celtic Zodiac is based upon the cycle of the Moon, with the year divided into the 13 lunar months established by the Druid religion.

The Druids believed that the human race originally descended from trees, each tree being endowed with its own particular mystical qualities. They encoded these mysteries in a secret shamanic alphabet known as the Ogham...the origin of which is ascribed to Ogma, the Celtic God of Poetry and Eloquence. It is said that Ogma (son of the Dagda) created the Ogham for the learned and wise to use for inscription. Originally intended to be read from the bottom upwards (or occasionally carved from right to left), Ogham (also often written as "ogam") is pronounced as "AHG-m" or simply as "OH-em." It served as an alphabet for one of the ancient Celtic languages and may have originally been adapted from a form of sign language. The current understanding is that the names of the twenty major letters are also the names of twenty trees which were sacred to the Druids. The Ogham may still be seen carved into stone monuments of the Druid Era and is thought to have been a means for the Druids to leave secret messages for one another. The Ogham is sometimes referred to as "Crane Knowledge," due to the fact that Cranes form letters with their legs as they fly. On the whole, the Celtic society was based upon equality and balance between the male and female...the female Druidesses being symbolized by the Dryads who lived in the sacred trees.

Each Celtic Tree/Zodiac Sign corresponds to a given tree, a letter of the Ogham alphabet, a Guardian Animal, a Celtic God and other items such as gemstones.