The purpose of this chapter is to summarize, elaborate, and extend research on social relationships, health, and well-being in late life. We examine research on social relationships in eight sections. We begin with a general discussion in the first section of why it is important to study social relationships in the first place. In the process, we briefly review literature on social relationships, health, and psychological well-being. Although our primary emphasis throughout this chapter is on social relationships and mental health, we also discuss research on social relationships and physical health because a number of studies have revealed that physical health problems may create mental health problems (Cohen & Rodriguez, 1995). In fact, there is some evidence this may be especially true in late life (Blazer, 2002). In second section, we focus on why it is important to study social relationships specifically in late life. An emphasis is placed in this section on theories that deal with the ways in which social relationships may change over the life course. The third section deals with an important but frequently overlooked issue in the literature-how do new social relationships form? We examine this topic because many support-based interventions are designed to help people develop new social relationships. In fourth section, we highlight the benefits of receiving social support from others. Then, in the fifth section, we turn to the underdeveloped literature that deals with companion friendships. Companion friendships refer to social ties that are developed and maintained for the sole purpose of enjoyment and the sharing of mutually valued activities (Rook, 1987). The sixth section is devoted to problems that arise when older people find they are embedded in conflicted social relationships. This is important because, as we discuss below, many people seek help from therapists to deal with negative interpersonal relationships. The seventh section is devoted to exploring how social relationships differ by gender and race/ethnicity. In the process, we briefly touch on social relationships that arise within religious institutions. In the final section, we summarize the key points in our discussion. We also point to issues that we were not able to discuss and identify issues that need more attention as the literature on social relationships in late life continues to evolve.