This dissertation presents a normative intellectual history of the development of religious toleration in the Latin West. In the Middle Ages, canon lawyers and theologians provided biblical justifications for tolerating unbelievers within their societies. During the crusades, however, a doctrine of missionary warfare justifying religious coercion for the purpose of punishing idolatry gained currency thus violating toleration as a political and ecclesiastical norm. Out of this crucible a stronger doctrine of natural freedom and natural rights for infidels emerged, which became the basis for sixteenth-century Spanish Dominican arguments in defense of Amerindian rights and peaceful evangelization. According to the Spanish Dominicans, most notably Bartolom de las Casas, freedom, property, and political rule were protected by the theological doctrine of the image of God, which provided the objective safeguard for the subjective rights of individual persons and communities on the basis of natural equality. Their peaceful ethic of evangelization and use of the principle of toleration challenged and constrained the centuries-old doctrine and practice of religious wars against idolaters. The culmination of these opposed doctrines of religious coercion and religious toleration in the sixteenth century surfaced at the Valladolid debate from 1550 to 1551 between Las Casas and his principal adversary, Juan Gin s de Sep lveda.This dissertation examines the broad corpus of Las Casas' writings throughout his life to make the claim that his legal theory of religious toleration, which was wedded to a doctrine of natural rights for believers and unbelievers alike, provided a compelling justification for what came to be understood as the most important of human freedoms' immunity from coercion in religious matters. For believers, the freedom to preach meant greater ecclesiastical immunity from the material interests of the Crown and the authority to reform gravely sinful practices among Christians. For unbelievers, the right to freedom in religious matters meant immunity from the political judgments of Christians. Las Casas' theory of religious toleration offered an unprecedented defense of religious rights for persons in error. But it also identified limits to toleration in the case of human sacrifice thereby rescuing his view from moral relativism. Overall, the inseparability of the doctrine of infidel rights from the Christian legal theory of religious toleration among Spanish scholastic jurists generated a normative ideal that remains constitutive of a theological vision of human rights today: preaching the Gospel to all persons demands the genuine freedom of those persons and the struggle, even sacrifice, on the part of Christians, to protect it.