Abstract: *Emergency Department Interventions for Opioid Use Disorder Treatment* Authors: Cindy Parks Thomas PhD, Maureen T Stewart PhD, Cynthia Tschampl PhD, Kumba Sennaar MS, Neto Coulibaly MS, Daniel Schwartz BS and Judith Dey PhD Research Objective: Opioid-related morbidity and overdose deaths continue to be a significant public health problem. For individuals with opioid use disorder (OUD), the emergency department (ED) is a critical entry point to potentially access treatment. A growing strategy to improve access to care for OUD and other substance use disorders (SUD) is through the ED, with several hundred programs estimated to be in place. This study examined several models of ED-based interventions for OUD, identifying key features, population served, metrics for assessing effectiveness, barriers to, and facilitators of success, and lessons for future programs. Study Design: Case study of five ED-based OUD intervention programs in different US regions, representing a wide range of models and populations. Interviews with a range of stakeholders and staff, and document review. Population Studied: Emergency department staff, peer/recovery navigators, hospital administrators, community partners, and policy makers were interviewed about treatment of patients with OUD and other SUD. Principal Findings: A wide range of models successfully identify and initiate OUD treatment in the emergency department, and have established strong relationships with community partners for continued engagement. Programs vary in their origin and motivation (initial developers and funding), how they identify patients (by providers, electronic record alerts, community awareness campaigns, post overdose, patient request only), how they initiate treatment, how they use peer navigators or substance use navigators, relationship with community partners, and metrics used for success. Program informants report having continued during COVID, often with telephonic peer support, and treatment initiation. ED OUD programs are seen by communities and other stakeholders as filling an important gap in care. There are a wide range of navigator-type positions employed, where some are foundational to a program’s operations and others have more circumscribed activities. Success in enrolling patients in MOUD did not depend on navigators having lived experience. Many stakeholders have found these programs to begin to address the stigma of treating persons with OUD and SUD more broadly, and are using this as a model to move beyond OUD identification and treatment to other substances, such as alcohol use disorder (AUD) and stimulant use disorder. Challenges remain, including sustained funding for programs initiated through federal or state grants, and the best approaches to the role of navigator. Conclusions: ED-based OUD programs are an important component in promoting low-barrier OUD care, and are a model for identification and treatment of other substance use disorders. Many models of care are in place. Challenges include stigma among providers, sustainability beyond grant funding, and available treatment capacity in community programs for follow-up. Implications for Policy or Practice: As ED OUD programs proliferate, it will be important to understand the features of these programs, and their contribution to a program’s success. It is also important to identify the best metrics for evaluating such programs, for potential standardization.