This thesis examined the significance of two aspects of social life for psychological well-being among a community sample of older adults. I proposed, first, that the degree to which elders engage in both informal interpersonal relationships and formal social affiliations are directly and positively related to psychological well-being; second, that these relationships are mediated through two elements of the sense of mattering. Contrary to expectations, it was found that states of mattering do not operate as mediating mechanisms linking social engagement and depression. Instead, the findings suggest that perceptions of mattering play roles independent of social engagement in promoting psychological well-being. Further conceptual and methodological development of the concept of mattering are needed to better understand the ways in which it is linked to social relationships and how these possible interlinked factors promote optimal health outcomes.