The present study examines within- and between-person associations between emerging adults' daily time spent alone and their positive/negative affect during social interactions. We also consider whether motivations for seeking solitude (shyness, unsociability, avoidance) moderate these associations. Participants were 411 emerging adults (ages 18-26 years; 51% female; 52% ethnic minority) who reported on their motivations for solitude and completed daily reports of their time spent alone and positive/negative affect experienced during social interactions for 7 consecutive days. Among the results, multi-level modeling indicated that on days when emerging adults spent more time alone than usual, they experienced increased levels of high and low arousal positive affect when they interacted with others. Interactions between shy and avoidant motivations and change in time spent alone also emerged, with follow-up analyses indicating that for highly and moderately shy and avoidant emerging adults, days with more time spent alone than usual were associated with greater reports of anxious affect during social interactions. Findings suggest that although many emerging adults may find social interactions more enjoyable on days with increased time alone, those who actively seek solitude as an escape from perceived stressful or unpleasant social circumstances may not.