Data from the 1999 National Survey of America's Families (N = 35,938) were used to examine the relationship between family structure and child well-being. I extended prior research by including children in two-biological-parent cohabiting families, as well as cohabiting stepfamilies, in an investigation of the roles of economic and parental resources on behavioral and emotional problems and school engagement. Children living in two-biological-parent cohabiting families experience worse outcomes, on average, than those residing with two biological married parents, although among children ages 6–11, economic and parental resources attenuate these differences. Among adolescents ages 12–17, parental cohabitation is negatively associated with well-being, regardless of the levels of these resources. Child well-being does not significantly differ among those in cohabiting versus married stepfamilies, two-biological-parent cohabiting families versus cohabiting stepfamilies, or either type of cohabiting family versus single-mother families.