Understanding the relative importance of overconsumption and physical inactivity to excess weight gain among children and adolescents can contribute to the development and evaluation of interventions and policies to reduce childhood obesity. However, there has been debate on whether energy intake or energy expenditure is the dominant contributor to childhood obesity. This review article evaluated the available literature related to the relative contribution of energy intake and energy expenditure to the U.S. childhood obesity trend. The studies examined suggest that the primary determinant of energy imbalance is not definitive. The authors conclude that more research and better methods are needed to identify the relative contribution of energy intake and energy expenditure to obesity in the pediatric population.