Reason and Explanation develops a novel explanationist account of epistemic justification. Poston argues that the explanatory virtues provide all the materials necessary for a plausible account of justified belief. The justification of a subject's belief consists in the explanatory virtues of the entire set of the subject's beliefs in comparison with other sets of beliefs she could have. Poston's argument for explanatory coherentism involves a defense of the epistemic value of background beliefs, the development of a novel framework view of reasons, and the articulation of a mentalist, evidentialist account of explanatory coherentism. Poston also argues against foundationalist attempts to ground facts about justification in sense experience. He extends the argument against foundationalism by examining how a priori justification consists in one's overall explanatory position. Finally, Poston articulates a compatiblist position regarding the relationship between inference to the best explanation and Bayesianism.