Sexual jealousy functions to defend paternity confidence and is therefore expected to be a ubiquitous aspect of male psychology. Several lines of evidence confirm this expectation. Cross-cultural and historical reviews of adultery law reveal remarkable conceptual consistency: unauthorized sexual contact with a married woman is a crime and the victim is the husband. We find male sexual jealousy to be the leading substantive issue in social conflict homicides in Detroit. A cross-cultural review of homicide indicates the ubiquity of this motive. Social psychological studies of “normal” jealousy and psychiatric studies of “morbid” jealousy both suggest that male and female jealousy are qualitatively different in ways consistent with theoretical predictions. Coercive constraint of female sexuality by the use or threat of male violence appears to be cross-culturally universal. Several authors have suggested that there are societies in which women's sexual liberty is restricted only by incest prohibitions, but the ethnographies explicity contradict this claim.