We provide an overview of the Kaiser Permanente Community Health Initiative--created in 2003 to promote obesity-prevention policy and environmental change in communities served by Kaiser Permanente-and describe the design for evaluating the initiative. The Initiative focuses on 3 ethnically diverse northern California communities that range in size from 37,000 to 52,000 residents. The evaluation assesses impact by measuring intermediate outcomes and conducting pre- and posttracking of population-level measures of physical activity, nutrition, and overweight.