Nonsuicidal self-injury (NSSI) is a behavior recently added to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) as a condition for further study. In this dissertation, I present findings from three studies that inform the clinical description of NSSI as well as some of the cognitive and emotional aspects of NSSI. In Study 1, I examined data from a community sample of adult women who met proposed DSM-5 criteria for NSSI or subthreshold NSSI. The findings show that any experience with NSSI is associated with significant impairment. Further, they suggest that greater self-criticism may be a key variable capable of distinguishing between people who engage in more versus less frequent NSSI. In Study 2, I examined the extent to which cognitive deficits in inhibiting emotional information may characterize people who engage in NSSI. Although NSSI participants endorsed greater difficulty with negative thoughts relative to controls, the groups demonstrated no differences on a directed forgetting task. These findings are consistent with previous research on emotional reactivity and impulsivity in NSSI that shows a similar dissociation between self-report and behavioral-based results. In Study 3, I examined how people process NSSI images. Results suggest that people who engage in NSSI view NSSI stimuli as relatively non-aversive. This is in sharp contrast to healthy controls, who consider NSSI images as highly aversive. These finding are consistent with models of NSSI that regard self-injury as providing reinforcement (positive and negative). Overall, the findings from these studies add to the clinical description of NSSI and support its diagnostic validity. Our examination of the clinical characteristics of the NSSI as described in DSM-5 highlights the importance of assessing the presence of any NSSI behavior as well as highly self-critical thoughts. Importantly, we found no evidence of memory deficits in NSSI. Of great clinical concern, however, is the extent to which engaging in NSSI appears to erode the aversive nature of NSSI stimuli. Taken together, our findings support a model in which self-criticism may reduce the initial barriers to engaging in NSSI, with the mood benefits associated with NSSI subsequently serving to maintain it. / Psychology