The pathology of obesity is a complex process involving interactions among behavioral, environmental, immunologic, genetic, and epigenetic factors. This article gives a broad overview of obesity. The physiology of fat storage, influence of eating behaviors on obesity, and the genetic relationship between eating and food sources are discussed. Specific genes that have been associated with obesity are introduced, with information on leptin and genes such as FTO, GLUT4, and others. This synopsis of obesity expands into environmental influences and epigenetic factors. These include food selection, gut microbiota, pregnancy, and exercise. The nurse will gain specific knowledge to assist in tailoring therapies specific to clients who are working to overcome the long-term effects of this disorder.