The roots of adolescent management of peer interaction and its associated emotions are important for understanding adolescents’ socio-emotional functioning, yet there is a lack of observational studies with multiple informants.  The current thesis examined late adolescents’ attachment style with mother and self-reported, partner-reported and observed conflict behaviours with a close peer. 
 Forty-four adolescents (30 females; Mean age = 17.9 years, SD = .63) rated their attachment to their mother (anxious and avoidant attachment) at two different time points a year apart, scores were averaged.  Target adolescents were videotaped with a romantic partner or same-sex friend discussing two problems in their relationship. 
As hypothesized, friend dyads were more harmonious and less conflictual than romantic dyads on self-rated collaboration, observer-rated disagreements, and observed negative and positive emotions.  Attachment findings pertained primarily to romantic dyads as observed by partners and/or independent observers.  Adolescents avoidantly attached to their mother displayed more disagreements in shorter romantic relationships whereas those in longer relationships who were more avoidantly attached showed both less disagreement and negative emotions with their partners.  Adolescents more anxiously attached to mother, surprisingly however, exhibited less disagreement and negative emotion, and more positive emotion, opposite to hypothesis.  As well, adolescents more anxiously attached demonstrated less negative emotion during the discussion with friends.  These findings support the continued role of attachment with mother in late adolescents’ emotion regulation behaviors with close peers, especially romantic partners.  Future research directions and implications for clinical interventions for both parents and adolescents are discussed.