SUMMARYThis paper develops an economic analysis of infidelity concentrating on the question of how cheating behavior differs between men and women. We develop an expected utility model that borrows from evolutionary biology to form expectations regarding behavior towards infidelity. We use U.S. data from the General Social Survey (GSS) and a Probit model to assess some characteristics of the respondent and his or her spouse that determine the probability of having an extramarital affair. While biology may form basic preferences, some of our results are consistent with the view that people are able to act on more than their base biological instincts alone. Hence, economic theory has a role to play in the understanding of behavior relating to infidelity. More specifically, this study identifies age, social class, individual's own education and the spouse's educational attainment as underlying factors affecting infidelity behavior depending on gender. In general, we find that men and women respond differently to the costs and benefits of having an affair.