ABSTRACT Suicide is the second leading cause of death among young people age 14–24, and rates in this age group are increasing. Most suicide risk factors are distal (i.e., long-standing, static), thus informative regarding who is at risk, but not when. As such, our ability to reliably predict near-term suicide risk among vulnerable populations remains grossly inadequate. Studies consistently demonstrate a link between subjective sleep disturbances and the continuum of suicidality. Yet, sleep is a complex behavior that can be measured along multiple dimensions and at varying levels of analysis. Furthermore, little attention has been paid to the role of normative biological and psychosocial developmental processes that further contribute to dynamic changes in risk related to sleep disturbance. Such changes in sleep are particularly dramatic during adolescence. Studies also have not examined how sleep interacts with other known pathways, such as dysregulation in affective, cognitive and arousal-related systems, to lead to suicidality in vulnerable youth. We thus propose to conduct an 8-week prospective multi-method study of sleep health and suicidal thoughts and behavior in a transdiagnostic sample of ultra-high risk adolescents (14-18) who have recently enrolled in an Intensive Outpatient or Partial Hospitalization Program. We will capitalize on the extant clinical and research infrastructures to compare sleep-suicide associations and plausible affective, cognitive and arousal-related mechanisms using self-report, behavioral, lab task paradigms and physiology in adolescents at ultra-high risk for suicide.