The emphasis to understand how the physical environment impacts health behaviors (e.g., physical activity) related to chronic diseases such as obesity has largely been focused on adults. Indeed, large studies using assessments of physical environment have been validated among adult samples. However, the physical environment may impact children differently and indeed the environments in which children are or are not active may differ from that of adults. The Active Where? Project is designed to address this gap. This study uses individual interviews with children and parents 'in situ', thus allowing researchers to observe the them while using the enviornment to prompt questions and responses. Perceptions can then be probed more deeply and correlated with the actual environment. The study is expected to yield generalizable self-report and observational instruments that will be relevant to youth of a very wide range of ages and will supplement the set of adult instruments currently used in national and international research. The Active Where? study is a collaborative research project comprising three locations: San Diego, Cincinnati Children's Hospital Medical Cente, and Boston Children's Hosptial. The collaboration allowed for data collection in three diverse US regions, which increases the generalizability of findings.The Boston team is additionally interested in assessing the relationship between adolescents’ perceived environment and participants’ body mass index, physical activity, and characteristics of their neighborhood determined through 2000 census tract information (e.g., socioeconomic factors).