The rapid increase in the prevalence of obesity in children and adolescents is alarming, particularly in light of its many medical and psychosocial consequences. In this review, we discuss key concepts of nutrition and physical activity. Etiology, prevention, and treatment strategies are also discussed, focusing on the macronutrient content of the diet, portion control, meal patterns, physical activity, and sedentary behaviors. Television viewing, lack of physical activity, and intake of fast food and soft drinks are also examined as potential contributing factors in the obesity epidemic. Children should be helped to develop healthy nutrition and exercise habits early, since interventions are most effective when behaviors are still being formed.