Approximately 70% of adults in the United States have obesity or are overweight and at risk of developing obesity over time. Obesity is associated with an increased risk of morbidity and mortality; the economic impact of the health care costs associated with obesity is anticipated to have a profound, detrimental effect on the country's economy within the next several decades. A number of psychologists have dedicated their careers to understanding psychosocial and behavioral factors that contribute to weight gain. Others have used psychological theories as the foundation to develop and refine interventions that serve as the cornerstone of most effective approaches to weight loss. Still others have used psychological principles to inform prevention efforts and public policy initiatives believed to be critical to current and future efforts to control the growth of obesity. The articles included in this special issue highlight the substantial contributions that many psychologists have made to the contemporary understanding of the development and treatment of obesity in children, adolescents, and adults. These articles also lay the foundation for the role that psychologists can and need to play in arresting and, ultimately, reversing, obesity in the United States and around the world. (PsycINFO Database Record (c) 2020 APA, all rights reserved).