Social relationships are essential in shaping individuals’ health and well-being. Scholars are increasingly interested in the complexities of how various dimensions of social relationships relate to health outcomes. Do different aspects of social relationships impact health in distinct ways? Beyond the relationship itself, how do the characteristics of the people within those networks affect an individual’s health? And can one person’s health issues influence others through these social connections? This dissertation explores these complexities by examining the links between social relationships and health outcomes across various life stages and contexts. The first chapter explores the associations between ego-friends differences in educational expectations and adolescent depression symptoms. This study finds that there was no significant difference in depressive levels between adolescents who had similarly high expectations like their friends and those with similarly low-expectation friends. But when a mismatch exists, low-expectation adolescents had more depression symptoms than high-expectation ones. The second chapter turns to the neighborhood context, examining how different characteristics of social networks may buffer the negative effects of neighborhood disadvantage on self-rated mental health in older adults. Results show that the negative associations between neighborhood social disadvantages and mental health are less pronounced for older adults who have a higher proportion of their social ties residing in the same local area. However, the buffering role is notfound in the other two aspects of networks: network size and frequency of interaction. The third chapter investigates the relationship between exposure to a friend’s or family member’s suicide and adolescent substance use. Results show that adolescents exposed to suicide are significantly more likely to use substances, with a stronger association observed for marijuana use than for smoking. Together, these studies illuminate how social relationships can shape individual health outcomes in nuanced and complex ways. By examining peer expectations, neighborhood social networks, and exposure to trauma within close relationships, this dissertation advances sociological research on the social determinants of health. It also provides valuable insights for health policies and programs designed to leverage social networks for health promotion and risk prevention.