This issue of Endocrinology and Metabolism Clinics, guest edited by Drs. Caroline M. Apovian and Nawfal Istfan, is devoted to Obesity. Articles in this comprehensive issue include: Guidelines for Obesity Management; Obesity is a Disease; Pharmacotherapy for Obesity; Bariatric Surgery Mechanisms; Diabetes Treatment in the Patient with Obesity; Adipose Tissue: Inflammation and the Endocrine Organ; Behavioral Treatment of the Patient with Obesity; The Role of Macronutrient Content in the Diet for Weight Loss and Weight Maintenance; Substrate Oxidation and Brown Adipose Tissue; Brown and Beige Adipose Tissue: Therapy for Obesity?; Ethnic Differences in Diabetes Lipids HTN and Obesity; Genetics of Bariatric Surgery Outcomes; Leptin and Hormones: Energy Homeostatis; Bariatric Surgery Clinical Outcomes; Medical Devices for Obesity; Adolescent Bariatric Surgery; Psychological Aspects of Obesity; and Nutrient Timing.