PROJECT SUMMARY Suicidal thoughts and behaviors (STBs) are major public health concerns among adolescents. STBs have their initial onset during adolescence and rates increase drastically during this developmental period. To reduce risk for STBs in youth, research identifying modifiable targets for intervention is greatly needed. Sleep problems, and particularly insomnia?the most common sleep problem in adolescents, may be one such promising treatment target. Insomnia has been consistently and uniquely linked to STBs (i.e., beyond depression), is associated with STBs over the short term (e.g., days, weeks), and is very treatable. Cognitive behavioral therapy for insomnia (CBT-I) is a brief (4-8 session) intervention with proven efficacy (medium-large effects) for reducing insomnia severity in adolescents and adults. In addition, CBT-I has been found to reduce a range of co-occurring psychiatric symptoms in adolescents (e.g., depression) and suicide ideation in adults. Although CBT-I is an empirically supported treatment (EST) that is highly recommended for treating insomnia, many adolescents do not have access to this intervention. Digital (smartphone-based) versions of CBT-I (dCBT-I) have demonstrated efficacy similar to in-person CBT-I and are accessible to youth, especially during high-risk periods where the need for treatment is critical. One of the highest risk times for STBs is the three months after discharge from acute psychiatric care, which is also a time when youth may have limited access to ESTs (due to long waitlists, high costs, difficulty traveling to treatment). Digital versions of ESTs, like dCBT-I, are highly accessible and may fill this significant treatment gap. The goal of this project is to test a brief (6- session), empirically supported, and highly accessible version of dCBT-I, called SleepioTM, in suicidal adolescents with co-occurring insomnia during the high-risk post-hospitalization period. The SleepioTM program includes the primary components of in-person CBT-I in a highly accessible digital format (via smartphone app). Although CBT-I has demonstrated efficacy in adults and adolescents with insomnia and has been found to reduce suicide ideation among adults, it has not yet been tested with suicidal adolescents?a high-risk group that is typically excluded from CBT-I trials. The overall project goal will be achieved through the following aims: Examine the feasibility and acceptability of delivering dCBT-I, SleepioTM, to suicidal adolescents with co-occurring insomnia during the post-hospitalization period (Aim 1), and examine the effectiveness of dCBT-I for reducing insomnia severity (Aim 2; treatment target) and suicide (STB) outcomes (Aim 3; distal clinical outcome). In line with the National Action Alliance for Suicide Prevention priorities, this project addresses key questions: ?What interventions are effective [for reducing STB risk]? What prevents individuals from engaging in STBs?? The current project represents a unique opportunity to extend an EST to a high-risk population who are in critical need but have limited access to care. This program of research has the potential to significantly advance clinical science and to modernize the way the field treats suicidal youth.