Sexual drives are rooted in biology, but we don't act on them blindly. Indeed, as the eminently readable judge and legal scholar Richard Posner shows, we make quite rational choices about sex, based on the costs and benefits perceived. Drawing on the fields of biology, law, history, religion, and economics, this sweeping study examines societies from ancient Greece to today's Sweden and issues from masturbation, incest taboos, date rape, and gay marriage to Baby M. The first comprehensive approach to sexuality and its social controls, Posner's rational choice theory surprises, explains, predicts, and totally absorbs.