Social support can have significant stress-preventive and stress-buffering benefits for troubled individuals in everyday circumstances. Consequently, it is not surprising that many therapeutic and preventive programs enlist social support to address problems of child and family psychopathology, especially in the context of “two-generation interventions” that seek to improve child well-being by strengthening parental functioning and parent–child relationships. Home visitation programs are the best known of these two-generation strategies and have become the focus of state-level and national efforts to support families and prevent harm to children. The conclusions of basic research studies on social support converge significantly with the findings of evaluation studies of the impact of home visitation programs to yield important new insights into the conditions in which formal social support is likely to be beneficial, or ineffective, in improving child and family well-being. Both basic and applied research literatures emphasize the importance of linking formal social support to informal social networks in extended families, neighborhoods, and communities, and attending to the complex reactions of the recipients of support and the needs of support providers. These studies are reviewed and evaluated to highlight the connections between social support, developmental psychopathology, and social policy.