PROJECT SUMMARY/ABSTRACT Suicidal behaviors (ideation, planning, attempts) and non-suicidal self-injurious behaviors (NSSI) are highly prevalent among juvenile justice-involved transition-age (TA) youth. More than half of youth in the juvenile justice (JJ) system report suicidal ideation; one-third report a history of suicidal behavior. Black youth are disproportionately represented in juvenile justice and are also at increased risk of suicide, as rates of suicidal behavioral and death by suicide among Black youth have risen at an alarming rate, faster than other racial/ethnic groups. This increase has resulted in a number of government initiatives to increase suicide prevention efforts for Black youth. Reducing suicide risk among JJ-involved youth must occur in conjunction with interventions addressing their broader needs for reduced externalizing behavior and in ways that are culturally appropriate for Black youth. iKinnect is a paired mobile app platform that supports parents (in delivering) and youth (in receiving) evidence-based practices to reduce youth problem behaviors. Based on Multisystemic Therapy principles, iKinnect1.0 was originally designed to help youth with serious conduct problems. Results from a randomized controlled trial (RCT; N=72) demonstrated its efficacy in reducing externalizing behaviors and improving parent effectiveness. This fast-track proposal seeks to significantly expand iKinnect to prevent NSSI, suicidal behaviors (ideation, planning, attempts), and death by suicide in JJ-involved TA youth while continuing to decrease externalizing behaviors and prevent recidivism. Leaders in the area of suicide risk among Black youth and cultural appropriateness of interventions will guide these efforts. This 33-month fast track will include three primary phases of evaluation: (1) a proof-of-concept formative evaluation phase during which we will iteratively design, test, and build a central portion of iKinnect2.0 to achieve its usability, acceptability, and relevance (Months 1-10); (2) a product design-and-build formative evaluation phase, where we will design, build, and test all remaining features for iOS and Android phones, while also preparing the platform for clinical use (Months 11-23); and (3) a summative evaluation phase involving a pilot test (N=15) of iKinnect2.0 and an RCT (N=120) comparing iKinnect2.0 to an active control condition; and results will then be analyzed, reported, and disseminated (Months 24-33). We predict that iKinnect2.0 TA youth and parents will report a significantly greater decrease in suicidal and NSSI behaviors and in conduct problem behaviors in TA youth. Furthermore, iKinnect2.0 participants (TA youth and parents) will report significantly greater use of behavioral skills, as well as self-efficacy in coping with emotional distress and other challenging situations. iKinnect2.0 parents will report greater awareness of and confidence in applying evidence-based strategies to prevent suicide/NSS...