This paper analyzes the long-term economic determinants of the demographic transition using a large panel of countries since 1870. A simple theoretical framework accounts for the possibly nonmonotonic variations of fertility in the course of economic development. As predicted by unified growth theory, I find that primary schooling, rather than income or health-related variables, is the most robust determinant of the fertility transition. As regards the health transition, both education and income are significant determinants of mortality rates, but education alone accounts for the bulk of their time variation over the twentieth century. Thus, education can be viewed as the main long-term determinant of the demographic transition.