PROJECT SUMMARY/ABSTRACT The prevalence of suicidal thoughts and behaviors (STBs) in late childhood and adolescence is alarmingly high, yet scientific understanding of STBs in youth is surprisingly limited. The NIMH has recently highlighted an urgent need for research examining mechanisms of complex health risk behaviors, including suicide, and a prioritization of child health research using existing datasets. The proposed study addresses these and additional scientific priorities by capitalizing on the unprecedented methodological advantages of the Adolescent Brain Cognitive Development (ABCD) Study to examine patterns of neurobiological, behavioral, and psychological processes, measured across multiple units of analysis, that define distinct subtypes of youth experiencing STBs in late childhood, as well as longitudinal associations between subtypes and STBs over adolescent development. This proposal addresses several critical limitations of prior research on suicide. First, despite epidemiological data that STBs frequently onset and escalate in late childhood and adolescence, suicide research has focused primarily on adults. Second, studies of suicide are largely cross-sectional and consider a narrow set of self-report variables. Third, most research takes a variable-centered approach and assumes a single set of risk-relevant processes apply similarly to all individuals, despite theoretical and emerging empirical evidence supporting the existence of multiple ‘subtypes’ of suicidal individuals defined by distinct profiles of risk-relevant vulnerabilities. The current study addresses these limitations in multiple ways. First, the proposed work adopts a primarily person-centered approach to examine patterns across neurobiological, behavioral, and psychological domains that distinguish distinct subtypes of youth who experience STBs by late childhood (ages 9-10)—the age at which suicide becomes a leading cause of death. Second, this work will test prospective associations of suicide subtypes with trajectories of STBs into adolescence, including potentially differential risk for persistence of suicidal ideation and/or onset of suicidal behavior. The proposal also offers opportunity to examine similar questions in a Supplemental Aim among initially nonsuicidal children, to examine risk for new onset of STBs in the adolescent transition. Finally, the proposal is not reliant solely on self-report and uses multimodal measures across units of analysis, including some that are relatively novel for suicide research (e.g., neuroimaging). In line with NIMH strategic objectives, the study will pursue these aims in the ABCD Study dataset. This dataset offers novel opportunity to address the aforementioned limitations of suicide research with longitudinal data on a large, heterogeneous, national representative youth sample from late childhood into adolescence. The research has potential to reduce heterogeneity of suicide by revealing distinct suicide subtypes ea...