This study examined development of emotional support competence within close friendships across adolescence. A sample of 184 adolescents (53% girls, 47% boys; 58% White, 29% Black, 14% other identity groups) participated in seven waves of multimethod assessments with their best friends and romantic partners from age 13 to 24. Latent change score models identified coupled predictions over time from emotional support competence to increasing friendship quality and decreasing support received from friends. Friend-rated emotional support competence in adolescence predicted supportiveness in adult romantic relationships, over and above supportiveness in adolescent romantic relationships. Teen friendships may set the stage for developing emotional support capacities that progress across time and relationships into adulthood.