Project Summary Physical activity has been associated with several chronic disease markers for the past 25 years, and countless studies have tested interventions to improve physical activity of sedentary populations. Most of these intervention studies have attempted to improve physical activity behaviors by changing individual level drivers of activity, like motivation, attitudes, and self-efficacy for being active. Unfortunately, these efforts to change activity levels are often not sustained beyond the initial intervention period. One possible cause of this lack of sustainability is that insufficient attention was paid to environmental factors that facilitate physical activity. Thus, attention is shifting to more complex environmental and social contributions to physical activity, with the aim of identifying multi-level strategies to better target interventions to groups that need help. Very few tests of changing environment levels to increase physical activity exist in the literature. A focus on interventions at environmental levels, as called for by recent reviews as well as reports from the Institute of Medicine, might provide the long-term sustainable change that is needed to change physical activity in low-income populations. This project seeks to test a new multi-level, multi-component package to increase moderate intensity physical activity levels of people living in public housing developments. Our aims are to evaluate the effects of an intervention package focused on the environment level to produce changes in moderate physical activity among public housing residents. Furthermore, we will evaluate the added effects of an efficacy-tested individual-level eHealth phone program to produce further changes in moderate intensity physical activity. The design of this study is a prospective, cluster randomized controlled trial, with housing developments as the units of randomization. In this four group, factorial, cluster randomized controlled trial, we will compare an environmental intervention alone (E only), an individual intervention alone (I only), an environmental plus individual intervention (E+I), all against a control group. Mediation and moderation of our intervention will be assessed. Lastly, we will assess factors from the Consolidated Framework for Implementation Research domains to examine future implementation of a multi-level physical activity intervention among key informants in public housing developments.