AbstractOvereating is a relative term. It refers to the consumption of an energy intake that is inappropriately large for a given energy expenditure, thus, leading to obesity. There are several key environmental and cultural factors that have converged in the past few decades to markedly increase the risk of both active and passive (inadvertent) overeating. Chief among these are the increased availability and promotion of cheap energy‐dense diets (usually high in fat) and the transition toward extremely sedentary lifestyles. The importance of considering these factors together must be stressed. Data ranging from highly controlled metabolic studies to large‐scale epidemiological and ecological analysis illustrate the strong interactions between diet and physical activity in relationship to the over‐consumption of energy. Overeating of certain specific dietary components may also lead to health risks. Obvious examples are saturated and trans‐fatty acids. More recently attention has switched to high glycemic foods and to n‐6 fatty acids. Theories that excess consumption of these may be independent risk factors for obesity and ill health remain controversial but merit closer examination and additional research. The main barriers to changing widely prevalent overeating include the following: public and corporate ignorance about the effects of energy‐dense diets in inducing passive over‐consumption, commercial willfulness concerning energy density and portion sizes, and public ignorance about the profound health effects of inactive lifestyles. These represent key targets for the design of public health initiatives.