For a long while, social scientists believed that religion would melt away in the face of modern, rational society. Maybe religion had been important in the formation of human societies, but soon those outdated beliefs and customs would be replaced. Yet now, at the beginning of the 21st century, it is clear that religion is not going anywhere. Americans, as with most of the world, are remarkably religious. Traditional faiths are vital and growing, and new religious entrepreneurs are establishing novel boutique religions at a remarkable pace. The question for believers, non-believers and social scientists in-between is why.