Project Summary/Abstract The overarching goal of the Greater Southern California Node (GSCN) of the National Drug Abuse Treatment Clinical Trials Network (CTN) is to expand access to and improve outcomes of treatments for substance use disorders (SUDs)?with a special emphasis on opioid use disorder (OUD) ?by collaboratively developing and testing effective and sustainable interventions for OUD that can be delivered in diverse healthcare settings. To achieve this goal, we have assembled (1) local, regional, and state-wide healthcare networks that serve millions of individuals, (2) investigators who have conducted seminal work on development and testing of pharmacological and behavioral interventions for SUDs, and (3) researchers with expertise in implementation strategies, data science, and innovative technologies to support treatment delivery and related research. Building upon investigators' past and current efforts, the specific aims of GSCN are: Aim 1. Lead and contribute to the development of new research protocols designed to increase access to treatments for OUD and to improve treatment outcomes; Aim 2. Support and participate in multi-site CTN projects and other CTN activities; and Aim 3. Disseminate research findings and provide innovative training to impact clinical practice. The GSCN research agenda will initially focus on four priority areas: (1) developing and testing effective medication and behavioral interventions for OUD and related comorbidities, (2) applying implementation science to deliver and expand OUD treatment in multiple healthcare settings, (3) leveraging eHealth (e.g., electronic health record systems) and data science for discovery and generation of innovative hypotheses and approaches to improve treatment for OUD, and (4) building on mHealth (e.g., smartphone- assisted interventions) and other technologies (e.g., telemedicine) to expand OUD treatment access and utilization. The GSCN research agenda reflects its capacity to collaboratively expand CTN efforts to develop and implement innovative approaches to improve treatment for OUD and other SUDs.