In the last five decades, ethical theory has been preoccupied by a turn to reasons. The vocabulary of reasons has become a common currency not only in ethics, but in epistemology, action theory, and many related areas. It is now common, for example, to see central theses such as evidentialism in epistemology and egalitarianism in political philosophy formulated in terms of reasons. And some have even claimed that the vocabulary of reasons is so useful precisely because reasons have analytical and explanatory priority over other normative concepts-that reasons in that sense come first. Reasons First systematically explores both the benefits and burdens of the hypothesis that reasons do indeed come first in normative theory, against the conjecture that theorizing in both ethics and epistemology can only be hampered by neglect of the other. Bringing two decades of work on reasons in both ethics and epistemology to bear, Mark Schroeder argues that some of the most important challenges to the idea that reasons could come first are themselves the source of some of the most obstinate puzzles in epistemology: about how perceptual experience could provide evidence about the world, and about what can make evidence sufficient to justify belief. Schroeder shows that, along with moral worth, one of the very best cases for the fundamental explanatory power of reasons in normative theory actually comes from knowledge.