Presence of support has repeatedly been linked to good long-term health outcomes based on demonstrations of better immune function, lower blood pressures, and reduced mortality (among others). Despite a massive literature on the benefits of support, there is surprisingly little hard evidence about how, and how well, social support interventions work. Using a computerized search strategy, 100 studies that evaluated the efficacy of such interventions were located. The presenting problems ranged from cancer, loneliness, weight loss, and substance abuse to lack in parenting skills, surgery, and birth preparation. For the purpose of review and evaluation, studies were subdivided into (1) group vs. individual interventions, (2) professionally led vs. peer-provided treatment, and (3) interventions where an increase of network size or perceived support was the primary target vs. those where building social skills (to facilitate support creation) was the focus. On the whole, this review provided some support for the overall usefulness of social support interventions. However, because of the large variety of existing different treatment protocols and areas of application, there is still not enough evidence to conclude which interventions work best for what problems. Specific methodological and conceptual difficulties that plague this area of research and directions for future research are discussed.