Determining the ultimate authority for Christian doctrine is both an issue of fundamental importance and can be seen as a particular manifestation, in the field of theological inquiry, of a more general epistemological problem, namely the problem of the criterion. After articulating this philosophical problem in theological terms, the main candidates for sources of authority in matters of doctrine – Scripture, tradition, reason, and experience – will be examined. Some major problems associated with taking any of the latter three as the ultimate source of authority will then be discussed, noting especially their inability to provide an adequate solution to the problem of the criterion. It will then be seen that Scripture fares better through a discussion of the notions of inspiration and self-authentication and their relationship to the internal witness of the Holy Spirit, drawing especially on contemporary work in theology and religious epistemology. The paper will close with a brief and selective look at some proponents of the primacy of Scripture from within the Anglican tradition. This paper will argue that Scripture is uniquely suited to act as a final authority for Christian theology in that, through the work of the Spirit, it brings its own evidence with it, avoids the serious philosophical and theological problems that result from taking another source as final, and fits seamlessly within the larger theological framework of God’s self-revelation in the economy of salvation. As such, it is my contention that Scripture should be regarded as the ultimate source of authority for Christian doctrine.