PROJECT SUMMARY/ABSTRACT The proportion of children with mental health conditions who get mental health care (e.g., psychotherapy, medication) has varied significantly between states for over a decade. Accordingly, the Health Resources and Services Administration (HRSA) recognized the utilization of children’s mental health services as a national concern by making it one of the National Outcome Measures for Maternal and Child Health. Unfortunately, it is unlikely this issue will improve without understanding how state-level factors that support utilization of mental health services by children. One potential factor may be state policy. Prior research has focused on how sociodemographic characteristics influence the geographic variation in the utilization of children’s mental health services, not the influence of state policies. The proposed mixed methods study will begin to address this knowledge gap by using tools from the field of implementation science and health services research. The study will use a modified framework based on Raghavan et al.’s Policy Ecology of Implementation Framework and Andersen’s Behavioral Model of Health Services Use to identify state policies that are perceived by policymakers as impacting the utilization of children’s mental health services. This study will determine policymakers’ perceptions of policies that influence utilization of children’s mental health services using a modified Delphi method (Aim 1) and investigate the association between state policies and state-level utilization of child mental health services (Aim 2). We will build upon a NIMH-funded center focused on strategies for states to improve systems affecting children (P50 MH113662-A1 PIs- Hoagwood, McKay) by leveraging mentorship from the team and findings from stakeholder surveys and interviews conducted as part of the center. The proposed research and training plan will allow the fellowship applicant to receive training in: 1) mental health services research and implementation science, 2) policies that influence the children’s mental health services system, 3) mixed methods research, and 4) scholarly writing and research dissemination. This training plan will support successful completion of the project and prepare the application for a career as an independently funded mental health services researcher dedicated to improving access and utilization to mental health care for children and families through local, state, and federal policy. The proposed project is consistent with the priorities set forth by the NIMH Strategic Objectives (4.2) and use tools from implementation research to broaden the public health impact of research and inform the development of state policy environments that support the uptake of evidence-based mental health treatments for children and families.