We develop a general model of paid and unpaid sexual exchanges in which any adult may supply or demand sex, depending on individual heterogeneity and labor market opportunities. Prices and participation are determined endogenously, and selection into the sex market shapes its composition, generating feedback effects on individual behavior. Without imposing gender roles, the model accounts for observed gender differences in paid sex, as well as the decline in sexual activity despite more liberal norms. It generates testable predictions on how market conditions and the expansion of digital sexual opportunities shape sexual exchanges and influence both supply and demand.