In this report the National Institute for Health Care Management Foundation (NIHCM) and the Association of State and Territorial Health Officials (ASTHO) focus on selective, exemplary collaborations between state health agencies and health plans to reduce overweight and obesity in children. The idea of collaboration is simple. Partner A agrees to work with Partner B on a project of shared interest. However, collaboration is more complicated in practice. Partners may experience cultural conflict, competition, and lack of trust. Nevertheless, as this report demonstrates, collaborations have the potential to produce significant value in the prevention of health problems associated with obesity. A successful collaboration can lead to better outcomes than either partner could produce on their own. This report profiles three case studies of collaborative obesity prevention programs that involved both organizations' key clients. As entities interested in promoting the health of the populations they serve, health plans and public health agencies are logical partners in the fight against childhood obesity. In addition, research revealed several unique collaborations between stakeholders other than health plans and state health agencies, such as academic institutions, state education agencies, businesses, and others. To illustrate the scope such broader partnerships can achieve, a fourth case is presented briefly in this report. The purpose of this report is to describe leading collaborations between state health agencies and private health plans in addressing childhood obesity. A technical appendix provides the structured instrument. (Contains 6 figures.) [This publication was co-produced by the Association of State and Territorial Health Officials (ASTHO) and made possible through cooperative agreements with the Centers for Disease Control and Prevention's (CDC) Division of Partnerships and Strategic Alliances.]