Social interactions are critical for the health and well-being of all group-living primates, including humans, across the lifespan. Social stressors, such as perceived criticism and rejection, are common triggers of nonsuicidal self-injury (NSSI). Social processes may thus have a central role in the etiology and maintenance of NSSI. Using the Research Domain Criteria (RDoC) framework for systems for social processes, the chapter presents recent findings on NSSI, mapping them onto the four constructs: affiliation and attachment, social communication, perception and understanding of self, and perception and understanding of others. The chapter also discusses available research related to NSSI for the respective units of analysis (genes and molecules, physiology, neurocircuitry, behavior, and self-report), focusing on the effects of social exclusion, rejection sensitivity, and negative social bias. The chapter also includes an overview of overlapping features related to social exclusion and rejection sensitivity between NSSI and borderline personality disorder, a condition characterized by interpersonal difficulties. This chapter provides an account of evidence-based assessment and intervention areas of social processes in NSSI together with recommendations and future directions. The chapter concludes that social processes are relevant to NSSI across the RDoC constructs and units of analyses. Social difficulties, social problem-solving, and experiences and interpretations of social situations need to be included in the conceptualization of how NSSI is developed and maintained and ultimately assessed and treated. In an effort to bring such conceptualization to life, a case example illustrates how an understanding of social processes may guide assessment and treatment of NSSI.