Evidence is cited showing that overweight is a health hazard, but that this is primarily true only when the excess weight is due to an excess accumulation of adipose tissue. Diagnosis of frank obesity should be established by a careful interpretation of height-weight tables and of all other pertinent data. Although many factors play an etiologic role, obesity can occur only when caloric intake exceeds caloric output, and can be obviated only when this imbalance is reversed. Therefore prevention of weight gain, which should receive increasing attention, and also satisfactory weight loss, both require that caloric output be increased through added physical activity and that caloric intake be decreased through diminished consumption. Success depends on recognizing the fallacy of all misleading misinformation, and on establishing permanent habits of regular exercise and of moderation in eating and drinking. Suggestions are made that can be effective guidelines to a commonsense program of weight control.