Female juvenile offenders exhibit high levels of anger, relational aggression, and physical aggression, but the population has long been ignored in research and practice. No anger management treatments have been developed specifically for this population, and no established anger management treatments are empirically supported for use with delinquent girls. Thus, to alleviate anger and reduce the frequency and severity of aggressive behaviors in this underserved population, we developed the gender-specific, Juvenile Justice Anger Management (JJAM) Treatment for Girls. This cognitive-behavioral intervention was adapted from the Coping Power Program (Lochman & Wells, 2002), a school-based anger management treatment for younger children that has established efficacy and effectiveness findings with its target populations. This paper describes how the content of JJAM was developed to meet the unique needs of adolescent girls in residential juvenile justice placements. It also traces the process of developing a manualized treatment and the steps taken to enhance efficacy and clinical utility. An overview of the treatment, a session-by-session outline, an example session activity, and an example homework assignment are provided. A randomized controlled trial is currently being conducted to evaluate the efficacy of the JJAM Treatment for Girls.