Objective: The objective of this study was to determine the environmental features that best support aging in place. Method: We conducted a realist synthesis, a theory-driven interpretive method of evidence synthesis, of 120+ articles (published 1991-2011) that attempts to explain how place may influence older adults’ decisions about mobility (e.g., physical activity). We developed an initial program theory, reviewed the literature, identified outcomes, analyzed and synthesized patterns, and created a final program theory. Results: Safety was a central mechanism, serving as one of the bridges between environmental components (e.g., connectivity, aesthetics, retail and services) and decisions about mobility. Population density, sidewalk presence, and park proximity did not emerge as key factors. Discussion: Safety considerations are one of the most prominent influences of older adults’ decisions about mobility. Street connectivity, pedestrian access and transit, and retail and services were also important. These factors are amenable to change and can help promote mobility for older adults.