Dimensions of emotion regulation in nonsuicidal self-injury and suicide in adolescents. Deaths from suicide continue to be a major public health concern, particularly among youth for whom suicide ranks as the second leading cause of death. Despite growing research on suicide, knowledge about the proximal behavioral and psychosocial mechanisms that facilitate the development of suicidal thinking is limited. Nonsuicidal self-injury (NSSI) is the intentional destruction of body tissue without suicidal intent, typically cutting or burning the skin, and has been identified as a particularly robust risk factor for suicide. Studies find that more than 20% of adolescents report engaging in NSSI, placing many at elevated risk for suicide. Remarkably little is known about the temporal course of NSSI and suicide ideation, or about how and why NSSI confers its risk for suicide. Emotion regulation deficits are associated with both NSSI and suicide ideation/behaviors but have rarely been studied in the temporal relationship between NSSI and suicide. Furthermore, it is not known which emotion regulation deficits are more salient for NSSI, and identifying specific deficits will aid prevention and intervention efforts. The proposed study aims to fill these knowledge gaps through a 12-month longitudinal study of 650 non-clinical, unselected adolescents between the ages of 14 and 17. The current study proposes that specific emotion regulation deficits will strongly associate with NSSI; specifically, lack of emotional clarity, lack of access to emotion regulation strategies, and poor cognitive reappraisal as measured by self-report, and decreased cognitive control for emotions as measured by a behavioral task. Additionally, the proposed study expects that NSSI behavior will associate with emotion regulation deficits to predict severity of suicide ideation, measured both explicitly with self-report and explicitly with a behavioral task, at follow-up points. Adolescents in 9th-11th grades will be recruited to complete a research protocol of self-report and behavioral measures at their home schools at baseline, 6- and 12-months post baseline. Tests of the difference between two dependent correlations coupled with effect size estimates will be used to determine which emotion regulation deficits most strongly associate with NSSI. SEM will be used to estimate cross-lagged panel models to examine how NSSI behavior associates with emotion regulation deficits over time and to examine how NSSI and emotion regulation interact to predict severity of suicide ideation over time. The results will provide essential information to the field of suicide prevention; there is potential to significantly impact clinical practice by identifying specific dimensions of emotion regulation that may be a marker of suicide risk that can be translated into assessment and intervention techniques.