Youth experience various physiological and psychosocial changes as they enter early adolescence, which are compounded by significant changes in the experience and expression of emotion (Rosenblum & Lewis, 2003).  Difficulty learning to modulate and manage emotional experiences is believed to underlie many emotional and behavioural difficulties (Thompson & Goodman, 2010).  Indeed, emotion dysregulation has been associated to a host of psychosocial difficulties, while adaptive emotion regulation (ER) has been linked to well-being and social functioning (e.g., Silk, Steinberg, & Morris, 2003).  Gottman and Mettetal (1986) proposed that early adolescents develop their ER skills as they explore and analyze their emotions in conversations with close friends, relationships that grow increasing important in early adolescence (Rubin, Bukowski, & Parker, 2006).  The intimate nature of early adolescent friendships likely stimulates frequent emotion-laden discussion and friends’ responses in these discussions can help or hinder the development of ER skills. This work explored the developmental course of ER in early adolescence, how emotion socialization experiences with best friends impacted ER, and how such translated to adjustment.  This longitudinal study followed 253 5th and 6th graders for one academic year.  Adolescent self-reports on the ER skills used when angry or sad/anxious, perceptions of how best friends responded to emotional displays, depressed affect and anxiety as well as peer reports about aggressive and prosocial behaviour were collected.   Growth curve and path analytic methods were used to model initial levels and changes in latent ER constructs over time as well as predictors and outcomes of regulatory skills.  Results showed that early adolescents’ use of ER skills was reflective of the emotional turmoil marking this developmental period; relative to the few significant decreases in the use of maladaptive ER skills, youth showed many more decreases in the use of functional skills.  The ways in which close friends directly socialized emotion and supported ER’s positive development were similar to relationships observed in the parental emotion socialization childhood literature.  Finally, many more stable predictions from ER to internalizing forms of adjustment were apparent relative to those with aggression.  This study was the first to outline the influential role that best friends have on early adolescent ER.