Regular physical activity is important for both physical and mental health. However, less than half of Americans currently meet federal activity guidelines. Public neighborhood parks offer accessible infrastructure that can facilitate physical activity, and most urban U.S. residents live within a mile of at least one park. Many communities and organizations have tried to encourage park use and park-based physical activity by building new facilities or adding activity centers. However, until recently, there has been little research to understand whether these or other investments are increasing the use of parks for physical activity. RAND Corporation researchers have conducted multiple studies to examine park use and assess parks’ role in promoting physical activity. They found that whether residents visit their local parks and how they decide to use them can be related to a wide range of factors, including individual characteristics, such as potential park users’ ages and genders; neighborhood and environmental factors, including community poverty level and residents’ perceptions of park safety; and park factors, including the numbers and types of facilities and the availability of organized activities. To support these studies, researchers developed an innovative tool, System of Observing Play and Recreation in Communities (SOPARC), to assess park use and physical activity. They also conducted in-depth surveys of park users and neighborhood residents. Their efforts provide insights into how parks are currently being used and suggest ways in which parks might be enhanced to encourage more physical activity. This report describes the tool and the research findings and recommendations.