In 2005, The California Endowment (TCE), a California-based foundation, launched a five-year initiative called the Healthy Eating Active Communities (HEAC) program. Guided by a comprehensive logic model, the goal of HEAC was to demonstrate that disparities related to childhood obesity and diabetes can be reduced in communities that offer families accessible and affordable opportunities for healthy eating and physical activity. TCE funded six HEAC collaboratives in six low-resource, ethnically diverse communities to create policy and environmental changes to increase access to healthy food and physical activity opportunities for children and families. The afterschool setting (or sector) constituted one of five key settings (school, afterschool, neighborhood, healthcare, and marketing/advertising) that can influence children's nutrition and physical activity behaviors. To enable them to make policy and environmental changes to improve healthy eating and physical activity, the collaboratives received extensive training and technical assistance to increase their organizational capacity to do this work. The evaluation of HEAC was a prospective, longitudinal study that used a multimethod approach to assess the extent of environmental change in each sector. A comprehensive HEAC evaluation is described in another chapter. This chapter describes the HEAC afterschool sector initiative, reviews findings from the nutrition component of the HEAC afterschool evaluation, and concludes with strategies that were used to implement the five-year training and technical assistance intervention initiative. (author abstract)