(Vanderbilt University Press) In this comparative ethnographic study, the authors situate marital HIV risk within a broader exploration of marital and extramarital sexuality in five countries: Mexico, Nigeria, Uganda, Vietnam, and Papua New Guinea. They argue that in these settings, extramarital sex occurs not simply because men’s bodies demand it and women cannot stop them; rather, it is a social practice that, though officially secret, is actually widespread and widely acknowledged. Jennifer S. Hirsch is an associate professor of sociomedical sciences in the Mailman School of Public Health at Columbia University. Holly Wardlow is an associate professor of anthropology at the University of Toronto. Daniel Jordan Smith is an associate professor of anthropology and associate director of the Population Studies and Training Center at Brown University. Harriet Phinney is a lecturer at Seattle University. Shanti Parikh is an assistant professor of anthropology, Washington University in St. Louis. Constance A. Nathanson is a professor of Clinical Sociomedical Sciences and professor of Population and Family Health in the Mailman School of Public Health at Columbia University.