The purpose of this paper is to shed light on the causes of the rapid decline in the infant mortality rate in the United States in the period after 1963. The roles of four public policies are considered: Medicaid, subsidized family planning services for low-income women, maternal and infant care projects, and the legalization of abortion. The most striking finding is that the increase in the legal abortion rate is the single most important factor in reductions in both white and nonwhite neonatal mortality rates. Not only does the growth in abortion dominate the other public policies, but it also dominates schooling and poverty.