People have a fundamental need for positive and lasting relationships. This need to belong is rooted in evolutionary history and gave rise to the development of traits that enable individuals to gain acceptance and to avoid rejection. Because belongingness is a core component of human functioning, social exclusion should influence many cognitive, emotional, and behavioral outcomes and personality expression. This article summarizes recent evidence that social exclusion causes an assortment of outcomes, many of which depend on whether the excluded can gain acceptance or forestall possible distress. It highlights common overlap in physical and social pain systems and how a physical painkiller can reduce the pain of social exclusion. Finally, it shows how social exclusion moderates the effects of traits on cognition, emotion, and behavior. To appreciate personality processes in social contexts, scientists should consider how people respond to social exclusion and how the need to belong influences personality expression.