For decades, scholars have debated the Framers’ intentions in adopting the Establishment Clause. In this Article, Professor Noah Feldman gives an account of the intellectual origins of the Establishment Clause and analyzes the ideas that drove the debates over church and state in eighteenth-century America. The literature on the history of the Establishment Clause has categorized discrete strands of eighteenth-century American thought on church-state relations, divided by distinct motives and ideologies. Feldman argues that this is a mischaracterization and proposes instead that a common, central purpose motivated the Framers to enact the Establishment Clause-the purpose of protecting the Lockean value of liberty of conscience. Feldman begins by providing an archeology of the idea of liberty of conscience, from Luther and Calvin to Locke. He then presents his account and analysis of the intellectual origins of the Establishment Clause in eighteenth-century American thought. He considers possible uses of this history, then concludes with observations on the utility of using intellectual history in constitutional analysis of cases invoking the Establishment Clause.