This paper addresses the question of what role morally oriented behavior plays in the efficiency of market outcomes. This issue is as controversial in economics as it is in sociology. To get a better understanding of the problems and opportunities involved in morally oriented behavior in markets, I develop a typology that distinguishes four different forms of morality-based behavior and try to understand what consequences derive from these types of morally motivated action. The four forms I discuss I call “cooperation,” “group solidarity,” “blocked exchange” and “altruism.” There is a fifth – parasitic – type that I call “Trojan altruism.” I argue that the contested role of morality is rooted in the profoundly ambivalent consequences that morality has on market efficiency.