At one time, God was a bird. In ancient Egypt, Thoth was the Ibis-headed divinity of magic and wisdom. Winged divine beings--griffins and harpies--populated the pantheon of Greek antiquity, and Quetzalcoatl was the plumed serpent deity of the pre-Columbian Aztecs. It is said that in spite of--or better, to spite--this time-honored wealth of divine avifauna, Christianity divorced God from the avian world in order to defend a pure form of monotheism. This narrative, however, misses the startling scriptural portrayals of God as the beaked and feathered Holy Spirit, the third member of the Trinity who, alongside the Father and Son, is the "animal God" of historic Christian witness. Appearing as a winged creature at the time of Jesus' baptism (Luke 3:21-22), the bird-God of the New Testament signals the deep grounding of archi-original biblical faith in the unity of all things: divine life and birdlife, divinity and animality, spirit and flesh. This book calls this new but ancient vision of the world "Christian animism" in order to signal the continuity of biblical religion with the beliefs of Indigenous and non-Western communities that Spirit enfleshes itself within everything that grows, walks, flies, and swims in and over the Earth. To this end, it weaves together philosophy (Martin Heidegger, Rene Girard), theology (Augustine of Hippo, Hildegard of Bingen, John Muir), and the author's own birdwatching visitations (wood thrush, pileated woodpecker, great blue heron, American dipper, domestic pigeon) to argue that all things are alive with sacred personhood and worthy of human beings' love and protection. When God Was a Bird is a revisionist history of avian divinity in Christian thought in the hope that biblical religion can return to its earthly origins--and thereby enable environmental wellbeing in a time of rapid global warming, indeed, global dying.