Arians in the third century AD maintained that Jesus was less divine than God. Regarded as the archetypal Christian heresy, Arianism was condemned in the Nicene Creed and apparently squashed by the early church. Less well known is the fact that fifteen centuries later, Arianism was alive and well, championed by Isaac Newton and other scientists of the eighteenth-century Enlightenment. This book asks how and why Arianism endured.