Environmental justice addresses physical and social health issues related to the distribution of environmental benefits and burdens among populations. The lower levels of recreational physical activity and greater rates of obesity among economically disadvantaged and racial/ethnic minority populations may be a result of environmental conditions in neighborhoods and communities. Environmental (e.g., less access to recreational facilities, less attractive neighborhoods, greater safety concerns in neighborhoods, and limited choices of grocery stores) and policy (e.g., less access to physical activity programs and opportunities) factors could explain some of the observed income and racial/ethnic differences in physical activity and obesity. This paper will review the literature on disparities in physical activity and obesity and the reasons for these disparities, particularly related to the environment. The authors of this paper will develop a conceptualization of environmental and policy variables that could explain physical activity and obesity disparities and propose a research agenda.