This Article provides a brief analysis of the main shifts in Western law and legal theory in four watershed periods: (1) the Christianization of Rome and Romanization of Christianity in the fourth and fifth centuries; (2) the Papal Revolution of the twelfth and thirteenth centuries; (3) the Protestant Reformation of the sixteenth century; and (4) the Enlightenment of the eighteenth and nineteenth centuries. It shows how major shifts in dominant religious ideas transformed the legal ideas and institutions of their day. It concludes that, although recent secular movements have removed traditional forms of religious influence on Western law, contemporary Western law still retains important connections with Christian and other religious ideas and institutions.