In 1900 only six percent of unwed females engaged in premarital sex. Now, three quarters do. The sexual revolution is studied here using an equilibrium matching model, where the costs of premarital sex fall over time due to technological improvement in contraceptives. Individuals differ in their desire for sex. Given this, people tend to circulate in social groups where prospective partners share their views on premarital sex. To the extent that a society's customs and more reflect the aggregation of decentralization decision making by its members, shifts in the economic environment may induce changes in what is perceived as culture.