Actions that promote fairness are sometimes consistent with the pursuit of individual self-interest, sometimes not. The diner who leaves a generous tip at a favourite local restaurant, for example, may do so partly out of a sense of obligation to the waiter. But we need not invoke fairness to explain the tip, which is, after all, a prudent investment in obtaining good service in the future. In contrast, narrow self-interest cannot explain why travellers might leave tips in restaurants located along interstate highways. Because it is unlikely that they will ever visit these restaurants again, their failure to tip cannot affect the quality of service they expect to receive in the future. So it is hard to escape the conclusion that concerns about fairness must be implicated when diners tip on the road. Of course, merely to assert the existence of a sense of fairness does not really explain why people often set aside concern for narrow self-interest. It simply raises the more fundamental question of why people have a sense of fairness in the first place. It is this question I will discuss.