Among the most innovative approaches to reduce childhood obesity and increase active living are youth advocacy programs that, in addition to affecting community change, may also promote youth empowerment and development. A multidisciplinary evaluation team will conduct an evaluation of 10-12 local youth advocacy groups (collectively called "YEAH!") that involve youth in community action to combat obesity and advance active living. Youth Engagement and Action for Health (YEAH!) is a youth advocacy and community empowerment project of the San Diego County Childhood Obesity Initiative to engage local youth and adult mentors in advocating for neighborhood improvements in physical activity opportunities and access to fresh and healthy foods. YEAH! empowers youth to assess their environments, prioritize issues, and implement action plans advocating for change. The evaluation will involve approximately 120 youth from diverse communities in rural, suburban, and urban settings. At least eight groups will be set in low-income communities composed of youth at highest risk for obesity. This study will help inform the field about youth advocacy among the most vulnerable populations of youth in a variety of settings, including schools, community centers, after-school programs, and other settings where youth may be engaged and supported.