Deliberate self-harm is a clinically-important behavior commonly associated with borderline personality disorder (BPD). Yet, despite the clinical relevance and associated negative consequences of this behavior, there are very few empirically-supported treatments for self-harm specifically among individuals with BPD (the population most at-risk for this behavior), and short-term treatments for self-harm in general have not been found to be effective for patients with BPD. Moreover, the two treatments that have been found to be efficacious in the treatment of self-harm among patients with BPD (Dialectical Behavior Therapy, Linehan, 1993, and Mentalization-Based Treatment, Bateman &Fonagy, 2004) are difficult to implement in traditional clinical settings (as a result of their duration and intensity) and are not readily available in many communities. Indeed, the majority of patients with BPD are treated by clinicians in the community without highly specialized training in the treatment of BPD. Thus, there is a need to develop new treatments for self-harm among patients with BPD that are shorter, less intensive, and more easily transportable, with a particular emphasis on adjunctive treatments that may augment standard therapy provided by clinicians in the community. To this end, and drawing from literature on the emotion regulating function of self-harm, the PI developed a targeted, short- term, adjunctive group therapy for self-harm among women with BPD specifically focused on decreasing emotion dysregulation. This project aims to further develop this emotion regulation group therapy (ERGT), for which there is preliminary empirical support. This project will take place in two phases, consistent with Stages 2 and 3 of intervention development. The first phase (Stage 2) will involve the development of a refined protocol, detailed treatment manual, and adherence/competency rating forms. During this phase, 24 self- harming outpatients with BPD will receive ERGT. In the second phase (Stage 3), 60 self-harming outpatients with BPD will be randomly assigned to receive ERGT in addition to their ongoing individual therapy, or to continue with their individual therapy alone for the duration of the group. Outcome measures will target four domains: self-harm, general psychiatric symptoms, adaptive functioning, and the proposed mechanisms of change (i.e., emotion dysregulation and emotional avoidance). Data from this development grant will be used to prepare a large-scale treatment outcome study comparing ERGT to a more rigorous control group and, eventually, to extant empirically-supported treatments for self-harm among patients with BPD. Although deliberate self-harm is both most common and most severe among individuals with BPD, there are few efficacious treatments for self-harm within this high-risk clinical population, and those that do exist remain relatively unavailable in many communities. Therefore, ERGT was developed as an adjunctive treatment for self-harm among patients with BPD, designed to augment standard therapy for BPD by specifically targeting both self-harm behavior and its proposed underlying mechanisms. Given that most patients with BPD are treated by clinicians in the community without specialized training, the development of a short-term adjunctive group therapy that can effectively augment the ongoing treatment of community clinicians has great clinical and public health significance.