The world is aging at an unprecedented rate, with older adults representing the fastest-growing segment of the population in most economically developed and developing countries. This demographic shift leaves much uncharted territory for researchers who study social relationships and health. Social relationships exert powerful influences on physical health in later adulthood, a critical consideration given age-related increases in the prevalence of chronic health conditions and physical disability. A large body of research indicates that older adults report greater satisfaction with their social networks than do younger adults, and that they often take measures to minimize their exposure to negative social encounters. These emotionally satisfying and generally positive social ties afford some health protection against a backdrop of mounting physical limitations and play an important role when juxtaposed with the potentially health-damaging frictions that sometimes emerge in older adults’ social relationships. Although most older adults report that they are satisfied with their social ties, some older adults experience frequent conflicts or ambivalent exchanges with members of their social networks, and these experiences detract from their health. In addition, many older adults will experience the loss of one or more close relationships during the course of their lives, with ramifications for their health and, often, for the reorganization of their social lives over time. Understanding how both the strengths and vulnerabilities of close social relationships affect health and well-being in later life is an important goal, particularly in view of the accelerating rate of population aging worldwide.