Prevailing theories of fertility behavior do not explain what sustains fertility in industrialized countries. Extending James Coleman's concept of social capital, the authors argue that the social resource value of children is an important factor motivating child-bearing. Data for the United States from the 1987-88 National Survey of Families and Households are used to test hypotheses regarding how fertility intentions are influenced by the social resource value of children, the economic costs of children, and the effect of children on parental career. The social resource value of children emerges as a powerful predictor of fertility intentions across groups stratified by race, gender, union status, and parity. Children create social capital for parents, an important and previously underappreciated reason for why Americans want children.