Obesity affects 17 percent of children and adolescents and almost 36 percent of adults in the United States. Conservative estimates suggest that obesity now accounts for almost 20 percent of national health care spending. Until the obesity epidemic is reversed, obesity will continue to drive rates of chronic diseases such as heart disease, stroke, type 2 diabetes, and certain types of cancer. Cross-Sector Responses to Obesity is a summary of a workshop convened by the Institute of Medicine Roundtable on Obesity Solutions in September 2014 to explore models of cross-sector work that may reduce the prevalence and consequences of obesity. This report identifies case studies of cross-sector initiatives that engage partners from diverse fields, and lessons learned from and barriers to established cross-sector initiatives.