Guided by research and theory on sibling similarities and differences, this study explored the nature and correlates of 2 processes of sibling influence—social learning and sibling differentiation—during adolescence. Participants included 2 adolescent-age siblings (M = 16.29 years for older siblings and M = 12.59 years for younger siblings, respectively) from 166 two-parent African American families. Significant nonlinear associations between these two influence dynamics and some sibling relationship qualities were discovered. For sibling differentiation, but not social learning, these links were further moderated by gender composition of the sibling dyad. Additional analyses revealed that youths' reports of social learning were generally linked to smaller differences between siblings, whereas differentiation processes were linked to greater differences in siblings' individual characteristics.