Our understanding of Celtic astrology is based mainly on the speculations of modern authors--mostly drawn from classical Greek and Roman writings--and suffers from many misconceptions. European astrology uses the Greek model, containing many Babylonian and Egyptian elements. But Celtic astrology (and other Indo-European astrologies) developed earlier, with relationships to Middle Eastern systems, as well as their own independent forms. This well documented study takes a fresh look at the development of Celtic astrology and the Druids' systems of cosmology, astronomy and astrology. The author analyzes commentaries found in manuscript sources from antiquity to the Middle Ages, comparing them with cosmological and astronomical lore found in Celtic cultures. Ancient constellations, calendars, deities and rituals reveal a rich worldview.