In 1695 John Locke published The Reasonableness of Christianity, an enquiry into the foundations of Christian belief. He did so anonymously, to avoid public involvement in the fiercely partisan religious controversies of the day. In the Reasonableness Locke considered what it was to which all Christians must assent in faith; he argued that the answer could be found by anyone for themselves in the divine revelation of Scripture alone. He maintained that the requirements of Scripture were few and simple, and therefore offered a basis for tolerant agreement among all Christians, and the promise of peace, stability, and security through toleration. This is the first critical edition of the Reasonableness: for the first time an authoritative annotated text is presented, with full information about sources, variants, amendments, and the publishing history of the work. Also provided in the editorial notes are cross-references, references to other works by Locke, definitions of terms, and other information conducive to an understanding of the text. Though modern interest has focused particularly on Locke's philosophy and political theory, increasing attention is being paid to his religious thought. These different strands cannot be understood properly in isolation from each other: so the broader aim of this edition is to help towards an improved understanding of his religious thought in the context of his work as a philosopher, political theorist, and exponent of religious toleration. In his editorial introduction John Higgins-Biddle investigates how Locke's ideas developed, and offers a critical assessment of the three main contemporary and subsequent interpretations of Locke's religious thought, all of which are shown to be unsatisfactory.