This study examined daily interpersonal events with parents and friends and daily well-being among 589 ninth-grade students (mean age = 14.9 years) from Mexican, Chinese, and European backgrounds. Associations were examined using a daily diary methodology whereby adolescents reported on positive and negative interpersonal experiences and mood each day for 2 weeks. Analyses using hierarchical linear modeling revealed bidirectional associations between adolescents' daily social interactions and mood. Findings indicated gender differences in adolescents' reactivity to daily interpersonal events as well as in the strength of daily mood as a predictor of interpersonal events. Furthermore, the ratio of positive to negative events experienced daily was consequential for adolescents' daily mood. Findings have practical implications for adolescents' everyday functioning and potential long-term adjustment.