This 4-year, multi-informant longitudinal study (N = 480, initial age: 15) investigated the interplay between parental support, behavioral and psychological control, and adolescents' emotion regulation development. We examined reciprocal effects between parents and children, mothers' versus fathers' unique roles in emotion regulation development, and sex differences. Multi-informant data allowed us to compare effects of adolescent-perceived and parent-reported parenting. Finally, innovative analyses allowed us to disentangle between-family differences from within-family predictive processes. Parenting and emotion regulation were associated at the between-family and within-family levels, especially according to adolescent reports. Support primarily played a role between mothers and adolescents, and perceived behavioral control between fathers and adolescents. Sex moderation revealed that support played a more prominent role in mother-daughter than mother-son relationships, and that daughters experienced greater behavioral control. Child effects outnumbered parent effects, which might reflect the increasing equality of adolescent-parent relationships. Finally, adolescent-perceived parenting was a stronger correlate of emotion regulation than parent-reports, suggesting that adolescents' perceptions are a relevant source of information for research and practice. Consistent with the self-determination theory perspective on parenting, emotion regulation flourished when adolescents felt like mothers provided support, and fathers loosened behavioral control. These results are in line with the notion that mother-child relationships are supportive attachment relationships, whereas fathers provide "activation" relationships, challenging adolescents to regulate emotions autonomously by providing less explicit structure. (PsycINFO Database Record (c) 2019 APA, all rights reserved).