A book that challenges our most basic assumptions about Judeo-Christian monotheismContrary to popular belief, Judaism was not always strictly monotheistic. Two Gods in Heaven reveals the long and little-known history of a second, junior god in Judaism, showing how this idea was embraced by rabbis and Jewish mystics in the early centuries of the common era and casting Judaism's relationship with Christianity in an entirely different light. Drawing on an in-depth analysis of ancient sources that have received little attention until now, Peter Schäfer demonstrates how the Jews of the pre-Christian Second Temple period had various names for a second heavenly power—such as Son of Man, Son of the Most High, and Firstborn before All Creation. He traces the development of the concept from the Son of Man vision in the biblical book of Daniel to the Qumran literature, the Ethiopic book of Enoch, and the Jewish philosopher Philo of Alexandria. After the destruction of the Second Temple, the picture changes drastically. While the early Christians of the New Testament took up the idea and developed it further, their Jewish contemporaries were divided. Most rejected the second god, but some—particularly the Jews of Babylonia and the writers of early Jewish mysticism—revived the ancient Jewish notion of two gods in heaven. Describing how early Christianity and certain strands of rabbinic Judaism competed for ownership of a second god to the creator, this boldly argued and elegantly written book radically transforms our understanding of Judeo-Christian monotheism.