We develop a theory of fertility, distinguishing the choice to have children from the
choice of the number of children. The deep parameters of the model are identified using
three facts of the 1990 US Census: (1) fertility of mothers decreases with education;
(2) childlessness exhibits a U-shaped relationship with education; (3) the relationship
between marriage rates and education is hump-shaped for women and increasing for
men. We estimate that 2.5% of American women were childless because of poverty
and 8.1% were childless because of a high opportunity cost of childrearing. Over time,
we show that historical trends in total factor productivity and in education led to a
U-shaped response in childlessness rates while fertility of mothers decreased.