Emotion development processes have long been linked to social competence in early childhood but rarely have these associations been examined in middle childhood or with relational outcomes. Guided by theories of interpersonal relationships and emotion socialization, the current study was designed to fill these gaps by examining a longitudinal process model indirectly linking emotion development to friendship quality. Data were drawn from 336 children (179 girls, 65% White), their mothers, and their teachers across 3 time points spanning the ages of 5-10 years. A path analysis model was utilized to examine the way in which maternal emotion socialization indirectly affects children's friendship quality. Results supported the hypothesized model in which maternal emotion socialization strategies used when children were age 5 were associated with changes in friendship quality from ages 7 to 10 via changes in children's emotion regulation. Findings highlight the importance of emotional processes for relational outcomes in middle childhood.