How did our forebears begin to think about religion as a distinct domain, separate from other activities that were once inseparable from it? Starting at the birth of Christianity-a religion inextricably bound to Western thought- Jack Miles reveals how the West's "common sense" understanding of religion emerged and then changed as insular Europe discovered the rest of the world. In a moving postscript, he shows how this very story continues today in the hearts of individual religious or irreligious men and women.