Policies Project Abstract Policymakers have launched multiple initiatives to reduce inappropriate prescribing of opioid analgesics, prevent opioid misuse, improve access to evidence-based treatment for opioid use disorder, and decrease rates of opioid-related overdose morbidity and mortality. The efforts have been taken at various levels of government, across different systems, and at different stages of the crisis. These layers of policy adoption and implementation create challenges for identifying which strategies, or “bundle” of strategies, may be most effective in reducing opioid-related harms. A growing number of opioid policy data resources have become available, but all rely on a piecemeal approach to select the specific policies covered. This project will develop an organizing classification framework for opioid policy surveillance and use the framework to improve the existing addiction policy data infrastructure and enhance our scientific understanding of the determinants of policy adoption and implementation. Using established best-practices from implementation science and legal epidemiology, we will develop a taxonomy for describing, reporting, and organizing the opioid policy landscape and assess the taxonomy’s relevance for broader addiction policy surveillance. We will also map existing opioid policy data resources within the taxonomy to identify where there are needs for new or improved opioid policy surveillance. Within three categories of the taxonomy, we will identify where states are adopting relevant policies and where there are gaps in current policy approaches; within each of the three categories, we will assess what factors influence states’ decisions to adopt particular policy approaches. The project will help address limitations of existing opioid policy datasets; inform opioid policy development within a more holistic framework of substance use and social policy; and lay the groundwork for extending this project to broader application, with the ultimate goal of developing a policy surveillance system that can characterize distinct components of the addiction policy environment (local, state, and federal) with applicability to future drug crises. Study findings will help spur progress toward identifying strategies, or combinations of strategies, most effective in reducing opioid-related harms.