Human beings have an innate need to form caring social bonds and be loved by others. Thwarting this basic human need should have negative health consequences. This article begins by reviewing empirical evidence linking belonging threats to concrete health outcomes and medical conditions. Next, alterations in immune function and appetite regulation are examined as two peripheral physiological mechanisms that partially explain how threats to belonging impact health. Empirically supported interventions that attenuate threats to belonging are also discussed. Throughout, the article focuses on loneliness, marital distress, and lack of perceived social support as three indices of belonging threats because they are commonly studied in the health context. Improving belonging, via reducing loneliness and marital distress and increasing social support, should thus be a focus for policy makers.