Philosophers have debated for millennia about whether moral requirements are always rational to follow. The background for these debates is often what I shall call “the self-interest model.” The guiding assumption here is that the basic demand of reason, to each person, is that one must, above all, advance one's self-interest. Alternatively, debate may be framed by a related, but significantly different, assumption: the idea that the basic rational requirement is to develop and pursue a set of personal ends in an informed, efficient, and coherent way, whether one's choice of ends is based on self-interested desires or not. For brevity I refer to this as “the coherence-and-efficiency model.” Advocates of both models tend to think that, while it is sufficiently clear in principle what the rational thing to do is, what remains in doubt is whether it is always rational to be moral. They typically assume that morality is concerned, entirely or primarily, with our relations to others, especially with obligations that appear to require some sacrifice or compromise with the pursuit of self-interest.