A lack of physical exercise is often implicated in many disease processes. However, sedentary behavior, or too much sitting, as distinct from too little exercise, potentially could be a new risk factor for disease.  Eight papers appearing in the “American Journal of Preventive Medicine” highlight and analyze current research on sedentary behavior, especially the relevant behavioral science that must be better understood if such behaviors are to change over time to improve health outcomes. These reports, including especially important reviews of the problem of sedentary behavior in children and across nearly two dozen countries, add to the growing scientific discussion about whether sedentary behavior may be an independent risk factor for disease.  The authors highlight the fact that broad-reach approaches and environmental and policy initiatives are becoming part of the sedentary behavior and health research agenda. With the implementation of such initiatives, positive changes in sedentary time likely will result.