Body weight sits like a spider at the center of a web of health and disease. Excess weight predisposes an individual to the development of a host of chronic conditions. The higher the body mass index (BMI) > 25 kg/m2, the greater the prevalence of abnormal blood glucose, lipids and blood pressure; hypertension and cardiovascular disease; diabetes; many cancers; gallstones; sleep apnea; complications of pregnancy; infertility; and premature mortality. Under the current national guidelines, a BMI between 18 and 25 kg/m2 is considered optimal, and the best health experience is achieved by avoiding increases in weight during adulthood. Maintaining a healthy body weight, or losing weight, is a direct function of calories consumed and expended. Portion control is essential for weight maintenance. The percentage of calories from dietary fat has little relationship with weight maintenance, while low consumption of sugary beverages and trans fats and higher intake of dietary fiber appear to be helpful. Regular exercise and the avoidance of extreme inactivity, such as excessive television watching, are also integral strategies for weight control. A supportive social and physical environment are also important.