This article, originally written for a French audience, attempts to explain the American law of church and state from the ground up, assuming no background information. Basic legal provisions are explained. The relevant American history is periodized in three alignments of religious conflict: Protestant-Protestant, Protestant-Catholic, and religious-secular. Some frequently heard concepts are explained, distinguished, and related to each other-separation, voluntarism, equality, formal and substantive neutrality, liberty, toleration, and state action. Finally, the principal disputes over religious liberty are assessed in three broad areas-funding of religiously affiliated activities, religious speech (with and without government sponsorship), and regulation of religious practice. These disputes are reviewed in historical, political, and doctrinal terms, with brief comparisons to the substantially different French solutions to the same problems.