This chapter reviews the origins of the only evidence-based group therapy designed specifically to address NSSI, emotion regulation group therapy (ERGT). Based on the evidence that many individuals who engage in NSSI struggle with and try to avoid their emotions, ERGT was based on an acceptance-based conceptualization of emotion regulation. ERGT emphasizes the functionality of emotions and problems associated with deficits in the capacity to experience the full range of emotions, as well as the paradoxical consequences of efforts to avoid or control emotions. The ERGT model is presented, as is evidence supporting the efficacy of ERGT, including recent adaptations for nationwide dissemination in Sweden and for adolescents.