Over the past decade, the linkages between marriage and child well-being have attracted the attention of researchers and policy makers alike. Children's living arrangements have become increasingly diverse and unstable, which raises important questions about how and why family structure and stability are related to child outcomes. This article reviews new research on this topic, emphasizing how it can inform policy debates about the role of marriage in reducing poverty and improving child outcomes. It also pays special attention to new scholarship on unmarried, primarily low-income families, the target of recent federal marriage initiatives, to appraise the potential contributions of family research to ongoing policy discussions.