In recent years, experimental economists have complemented earlier research by psychologists on equity theory, altruism, and related theories, by studying the anonymous allocation of dollar prizes by experimental subjects. This research has helped us understand the nature of attitudes towards fairness, reciprocity, and other "social preferences," and how these attitudes interact with self interest. The author critically reviews some of this evidence and the prevalent interpretations of this evidence to suggest some general lessons and ideas for where further research would (...) be useful. (shrink)