Fertility rates in industrialized countries have long moved procyclically. Recently in the United States, however, fertility has fallen in economic expansions and risen during contractions. A simple economic model that emphasizes the distinction between male and female earnings in affecting fertility and the distinction between families with and without employed wives is able to reconcile these fertility movements. The model accurately predicts U.S. fertility rates many years after the sample period of estimation. These results suggest that postwar increases in the aggregate demand for labor raised the market earnings of young women and led to the rapid fertility declines of the last 20 years. The prospect is for continuing fertility decreases punctuated by countercyclical movements. 63 pp. Bibliog.