The recent dramatic increase in obesity has occurred more rapidly than can reasonably be explained by a change in physiological or genetic makeup of the individual, pointing to changes in the environment as likely contributors. The design and architecture of the physical environments where people live and work, the built environment has been suspected as a contributor to obesity by promoting a reduction in activity and an increase in food intake. The existing research, though, has investigated the nature of the overall built environment in which the individual resides and relates the characteristics of that environment to the individual's reported overall behavior. It does not relate actual environmental features to actual real time behaviors. Also, the nature of the environment is confounded with the nature of the individuals who choose to occupy the environment, often differing in socioeconomic status, race etc. Finally prior research has investigated environments that do not have a large range of variation. The proposed project is an exploratory study to develop the methodology and analytic techniques to address the relationship of the built environment to energy balance. The developed methods will then be employed to investigate the real time relationships of actual behavior to the characteristics of the exact environment in which the behavior occurs. The project will develop a method for assessing intake and activity empirically with triaxial accelerometers and 7-day diet diaries while monitoring the individuals' exact positions with Global Positioning System (GPS) data logging receivers. Geographical Information System (GIS) data bases will be accessed to establish the characteristics of the built environment at the point of the actual behavior. The project will develop a method to identify how the characteristics of the built environment are related to intake and activity. It will develop a method to ascertain how the same individual responds to different environmental characteristics. It will develop a method to ascertain how characteristics of the individual interact with the built environment to affect intake and activity. It will begin to explore activity, intake and built environment relationships in a wide range of environments. The epidemic of obesity is posing a significant danger to public health. By identifying how the built environment may be contributing to intake and activity, the proposed research should lead to a better understanding of the causes of obesity and routes for prevention and treatment.