In this article, Melanie Wasserman reviews the latest evidence about the causal link between family structure and children's economic and social outcomes. Going beyond the question of whether family structure affects child outcomes--a topic that's already been covered at length, including in previous Future of Children volumes--she examines how family structure differentially affects children. One important finding from recent studies is that growing up outside a family with two biological, married parents yields especially negative consequences for boys as compared to girls, including poorer educational outcomes and higher rates of criminal involvement. Wasserman describes mechanisms that may link family structure to children's outcomes, in terms of both the main effect and the differences between effects on boys and on girls. These include same-gender role models in the household and in the neighborhood, parental resources (including money, time, and more), parenting quantity and quality (with attention to how parents allocate their time to children of different genders), and the differences in how boys and girls respond to parental inputs, among other hypotheses. What can be done to ameliorate the effects of family structure on children's outcomes? Wasserman encourages policy makers to supplement the educational, parental, and emotional resources available to those children who are most at risk of experiencing the negative effects of nontraditional family structures.