The chapters in this volume aim to advance the discussion of the role of the a priori in philosophy by addressing four sets of issues. The first is whether intuitions provide evidence for philosophical theories, whether that evidence is a priori, and whether the results of experimental philosophy affect the evidential or a priori status of intuitions. The second is whether there are explanations of the a priori and what range of propositions can be justified and known a priori. The third is whether a priori justified beliefs are needed in order to avoid some skeptical worries. The fourth is whether certain recent challenges to the existence or significance of the a priori are successful.