Uses an economic model of fertility behavior to explain fluctuations in fertility rates and to predict future rates. It directs attention to two variables: family income and the opportunity cost of women's time. It predicts that women who earn higher wages in the labor market will have fewer children because the opportunity cost of their time with children is higher. As more women are employed the former positive relationship between business cycles and fertility breaks down, and fertility rates may move countercyclically. Estimation of the model concentrates on U.S. fertility trends since 1947. Forecasting based on this model indicates that the current downtrend in births is not a case of delayed births likely to be made up later. As long as women's real wages continue to rise and a large proportion of women are employed, continuing fertility declines can be expected. The societal implications of these declines are discussed.