This research project addresses two questions. How do social relationships and social support change with age? And when are social relationships most beneficial or harmful to health? To do this we examine three waves of the Social Relations, Age and Health study spanning more than 20 years, analyzing detailed changes in social relations using both monthly assessments and multiple informants. Specifically, this study (1) tests competing theories about age, social relations and health; (2) specifies the direction and shape of change in social relations over time; (3) tests the relative strength of the three hypothesized mechanisms of social contagion: induction, homophily, and shared environmental factors; and (4) examines competing exchange theories, e.g. altruism, developmental stake, support bank, well as their association with health disparities.