There is a growing consensus, long maintained by Derek Parfit, that there is an important distinction between what we have reason to do on the one hand, and what it is rational for us to do on the other. Philosophers are now realising that there is a conceptual distinction between rationality and normativity. Given this distinction, it thus becomes a substantive question whether rationality is genuinely normative; that is, whether there is any reason to do what rationality requires. While some philosophers have argued that we sometimes have reason to do what rationality requires, it is notoriously difficult to show that there are always universal and categorical reasons to do what rationality requires. But if it is not the case that there are always universal and categorical reasons to do what rationality requires, then rationality is not genuinely normative.This dissertation offers a vindication of the normativity of rationality. I maintain that there is a robust relation between rational requirements and normative reasons. In arguing for this claim, I develop what I call the reasons-sensitive view of rationality, according to which rational requirements are normative verdicts: they are second-order claims about what there is conclusive reason of rationality to do. This view explains why there are always universal and categorical reasons to be rational. So while we may not always have most reason to do what it is rational for us to do, there is always some reason—reasons of rationality—to do what it is rational for us to do. I then show how this reasons-sensitive view addresses and responds to what I diagnose to be the major sources of skepticism about the normativity of rationality.