One of the most provocative projects in recent analytic philosophy has been the development of the doctrine of externalism, or, as it is often called, anti-individualism. While there is no agreement as to whether externalism is true or not, a number of recent investigations have begun to explore the question of what follows if it is true. One of the most interesting of these investigations thus far has been the question of whether externalism has consequences for the doctrine that we have authoritative, a priori self-knowledge of our mental states. The papers in this volume, some previously published, some new, are representative of this debate and open up new questions and issues for philosophical investigation, including the connection between externalism, self-knowledge, epistemic warrant, and memory.