SUMMARY Social determinants of health are key influencers of health inequality and contribute to health disparities between populations and communities. Implementation science (IS) has particular potential to accelerate progress toward achieving health equity goals, and significant work has focused on implementation in settings that serve marginalized populations. Context is a central feature of IS, yet it is frequently poorly defined or goes unreported. When it is considered, attention to context is mostly focused on the inner setting in which the intervention is implemented, with relatively little consideration of how the outer context may impact implementation. Failure to fully measure outer context and to use those data to inform implementation efforts limits the applicability and generalizability of study findings to different populations, settings, and time periods. This supplement application under the OPTICC (Optimizing Implementation in Cancer Control) Center will meet this challenge by partnering with the six other ISC3 centers to create a set of outer context common data elements (OC-CDE) that will be collected for all centers. Our proposed Aim is to characterize the outer context of OPTICC's I-Lab and contribute to the OC-CDE database. We will conduct an environmental scan of outer context factors that may impact OPTICC I-Lab implementation outcomes and create an OC-CDE database in collaboration with ISC3 centers. For this process, we will meaningfully engage our I-Lab partners to not simply define state and county-level catchment areas for OC-CDE collection but also to explore how they might utilize these data and their impressions of its impact on EBI implementation. This input will inform OPTICC's center- wide use of causal pathway diagrams articulating the role of factors influencing how strategies work. We will utilize the HealthLandscapes database to collect select measures across the domains of interest, supplementing it with other publicly available data as needed. The final dataset will be uploaded into a shared REDCap database for analysis, manuscript development, and pilot planning. The final quarter of the project will be spent on data cleaning, development of the cross-center data repository, and publications, presentations, and pilot project planning. The primary deliverable for this phase I effort is the development of a database with outer context measures for each center's catchment area and the initial description of the outer context across participating centers. We also expect this work to yield a rich data asset, with engaged I-Lab partners, and a causal pathway positioning us to engage in cross-center pilot studies to advance health equity. This work will prepare centers for future opportunities to investigate the relationship of contextual factors to implementation strategy selection, successful implementation, and sustainment.