Abstract Juvenile justice-involved youth (JJIY), primarily adolescents ages 13-17, are a complex and highly vulnerable population who have high rates of psychiatric disorders, suicidality, trauma, and lower socioeconomic status. Minoritized youth (by race) are disproportionately represented among JJIY. Though the need for mental health services is pervasive among this population, only 20-25% of JJIY receive mental health treatment while involved in the juvenile justice system, with even lower rates among racial minorities. All of these factors are associated with poor sleep; further, poor sleep quality and insomnia are widespread among incarcerated adults. Yet, there has not been a systematic study of the sleep of JJIY, the correlates of sleep in this population, nor the options for implementing evidence-based sleep-focused treatments in various juvenile justice system settings. This is a critical gap in the literature, especially because sleep promotion is associated with reduced psychopathology. We propose a descriptive, mixed-methods study to 1) examine the nature and correlates of sleep among JJIY; 2) identify points of intervention in the juvenile justice system where sleep treatment can be delivered, personnel who can deliver it, and the resources needed to do so; and 3) identify strategies for effective translation and implementation of evidence-based sleep-focused interventions in system settings. We will conduct a cross- sectional survey of JJIY (13-17y; n=25 in residential placement, n=75 under community supervision, reflecting national rates). Youth will complete a daily sleep diary and a subset (n=40) wear actigraphy for 10 days. Parents and adult caregivers will be invited to complete a complementary survey (n=100). To obtain further information, we will invite 20 of the full sample of 100 youth to participate in one-on-one qualitative interviews. We focus on ages 13-17 given the rapid and interacting changes in sleep, emotion regulation, and behavioral regulation during this period. We will also conduct qualitative interviews with 20 individuals working in the juvenile justice system (residential counselors, probation officers, healthcare providers). Survey data will be preliminarily analyzed to inform the interviews. Then, in Year 2 we will conduct and analyze the interviews using Rapid Qualitative Inquiry, and we will conduct quantitative data cleaning and full analysis. We will rely on stakeholder-engaged research, which values community members as equitable research partners and may result in more sustainable and effective programs by tailoring the program to the community context. This work aligns with the NIMH Strategic Plan Objective 4.3: to conduct research that optimizes and improves access to existing programs that improve mental health services for underserved populations. This R21 will constitute the essential first step in a program of research that will include further developing and adapting existing sleep interventio...