Child support policies in the United States have expanded dramatically since the mid-1970s and now cover 1 in 5 children. This paper studies the consequences of child support for marriage and fertility decisions. I first introduce a model showing that child support enforces ex ante commitment from men to provide financial support in the event of a child, which (1) increases premarital sex among couples unlikely to marry, and (2) reduces the abortion rate, by lessening the cost of raising a child as a single mom. Using variation in the timing and geography of the rollout of U.S. child support laws relative to the timing of pregnancy, from 1977 to 1992, I find that marriages following an unplanned pregnancy are less likely to occur under strengthened child support laws, accounting for about a 7-8 percentage point reduction relative to a base of 38 percent. I find that the child support rollout reduced the abortion rate by 1-2 per 1000 women aged 15-44, off a base of 28, representing about 50 percent of the total decline in the abortion rate over this period.