Abstract: I argue that it can be rational to defer to an authority about what to believe or what to do even when doing so goes against one’s own reasoning. Indeed, such deference is rational in typical cases in which individuals treat others as authorities: for example, experts in a domain, interpersonal advisors, and religious traditions. I explain the interplay between authority, reason, and disagreement, and how rational faith gives rise to epistemic communities and governs their encounters with each other.