Nonmarital fertility – or having a child outside of marriage – has become an increasingly important phenomenon demographically, socially, and politically. Fully one in three US births were to unmarried women in 2000, compared to just 5 percent in 1960. This change has generated a great deal of concern. Many worry because unmarried mothers tend to be younger and less advantaged socially and economically than married mothers, and their children tend not to do as well as those living with two married biological parents. Others worry that the growing number of families formed outside of marriage is weakening the institution of marriage. Policymakers have introduced measures in recent years explicitly designed to reduce the number of births to unmarried women. The 1996 welfare reform legislation, Personal Responsibility and Work Opportunity Reconciliation Act (PRWORA), for example, includes incentives for states to reduce their rates of nonmarital childbearing, and reauthorization legislation includes resources to strengthen and promote marriage through outreach and counseling.