This study examined the relations among maternal socialization of positive affect (PA), adolescent emotion regulation (ER), and adolescent depressive symptoms. Two hundred early adolescents, 11–13 years old, provided self-reports of ER strategies and depressive symptomatology; their mothers provided self-reports of socialization responses to adolescent PA. One hundred and sixty-three mother–adolescent dyads participated in 2 interaction tasks. Adolescents whose mothers responded in an invalidating or “dampening” manner toward their PA displayed more emotionally dysregulated behaviors and reported using maladaptive ER strategies more frequently. Adolescents whose mothers dampened their PA more frequently during mother–adolescent interactions, and girls whose mothers reported invalidating their PA, reported more depressive symptoms. Adolescent use of maladaptive ER strategies mediated the association between maternal invalidation of PA and early adolescents’ concurrent depressive symptoms.