In this chapter, we review the benefits of gratitude to well-being, with particular attention to the social psychological mechanisms of this relationship. We first define gratitude at two levels of analysis—state and trait—and recommend useful assessments for gratitude. We then discuss how both correlational and experimental studies have shown that gratitude is an important characteristic of the good life. Current research has now turned to the mechanisms of this relationship: How does gratitude support well-being? We emphasize two complementary social psychological mechanisms that have received empirical support: cognitive and social. First, preliminary evidence supports the theory that gratitude interventions change cognitive processes related to appreciation. Second, both experiencing and expressing gratitude have a positive impact on one’s relationships. We conclude by explaining two theories that help organize the research on gratitude and provide direction for the future: Algoe’s Find, Bind, and Remind theory and our psychological amplification theory.