This article reviews literature fromthe health field investigating the characteristics of environments that support or hinder physical activity. This literature shows that physical activity is associated with objective and subjective measures of accessibility to recreational facilities and local destinations, as well as with neighborhood safety and visual quality. Walking and biking emerge as prominent forms of physical activity and occur primarily in neighborhood streets and public facilities, suggesting that building walkable and bikable communities can address health as well as transportation concerns. The studies help advance environment-behavior research related to urban and transportation planning. They identify behavioral and environmental determinants of physical activity and employ rigorous data collection methods and theoretical frameworks that are new to the planning field. The article concludes that multidisciplinary research will likely yield promising results in identifying the aspects of environments that can be modified to encourage physical activity and physically active travel.