In recent years, rising rates of obesity in the United States have generated concerns about the impact of the built environment on obesity. These concerns spurred community-based obesity interventions that center on land use, transportation, and urban design to increase physical activity and thereby reduce obesity. This thesis seeks to understand the role of planners in reducing obesity, specifically through planning physical activity environments. Public health and urban planning literatures demonstrate the challenges in reducing obesity through urban planning and form the basis of inquiry for this research. This thesis suggests that there are challenges in the planning process that make it difficult to reduce obesity. Second, this thesis argues that the tools needed to address obesity are different in low-income urban communities than in higher income suburbs. Ultimately, this thesis urges planners to mobilize against the fundamental causes of disease by taking a more contextualized approach to addressing obesity.