It is widely accepted that America is in the midst of an obesity pandemic (1,2). Substantial research is directed toward both understanding how and why this has occurred and toward identifying effective ways to prevent and treat obesity. Permanent behavior change is required for any change in body weight, but the extent of behavior change needed varies with the desired outcome. The term “energy gap” was coined to estimate the change in energy intake and energy expenditure behaviors required to achieve different body weight outcomes in individuals and populations (3). Since the original article about the energy gap, the term has become widely used (and misused) by researchers interested in both prevention of weight gain and treatment of obesity (3-14). It has been argued that the energy gap fails to consider that energy stores continue to increase with weight gain so that there is a cumulative energy gap that builds over time between obese and non-obese individuals so that small changes in eating and physical activity would be insufficient to reverse the obesity pandemic (13,14). The purpose of this commentary is to more precisely clarify the concept of the energy gap (or energy gaps) and discuss how the concept can be properly used as a tool to help understand and address obesity.