Most youth and adults in the U.S. do not meet recommended levels of physical activity, despite the significant and extensive health benefits associated with being sufficiently active. Interventions to increase physical activity are critical to improving an individuals' and population health. However, generally efficacious interventions may not be consistently effective across individuals. Personalized behavioral medicine in which interventions are tailored to the context in which individuals are attempting to improve health behaviors remains a nascent field. Among context factors, built and social environment factors within the home neighborhood are related cross-sectionally to individuals' physical activity (e.g., residents in more walkable neighborhoods are generally more active). However, cross-sectional observational studies do not identify whether or which environmental factors are facilitators or barriers to attempts to increase physical activity. The proposed InSPACE project examines whether and which home neighborhood built and social environment factors affect individuals' response to physical activity interventions. We propose to recruit and engage with 50+ physical activity intervention trials across the country to generate comprehensive and consistent measures of objective built (e.g., residential density) and social (e.g., median household income) neighborhood environment linked to individual participants within each trial. Advances in the availability of national spatial data and an innovative user-friendly tool to create and attribute environmental measures to anywhere in the U.S. (the Automatic Context Measurement Tool) makes InSPACE timely and feasible. Environmental, physical activity outcome, and demographic data will be harmonized across trials and pooled to allow for robust testing of environmental effect modification of physical activity intervention not possible within single trials. In addition, pooled data will allow for testing of whether critical individual-level demographic factors, such as age and race/ethnicity, interact with neighborhood environmental factors in affecting physical activity intervention outcome. Guided by an expert scientific advisory council, findings from InSPACE have the potential to rapidly and efficiently identify who will be responsive to existing efficacious physical activity interventions in what contexts and encourage innovation in changing interventions to better match individuals' environmental contexts when attempting to increase physical activity.