The rise in obesity rates over the past 30 y has been paralleled by increases in the portion size of many foods and the prevalence of eating away from home. Foods of particular concern are those that have a high energy density (kJ/g). Many well-controlled, laboratory-based studies have found that large portions of energy-dense foods can lead to excess energy intakes. This influence of large portions on energy intake has been supported by data collected in naturalistic settings. Further research is needed to explore strategies that can be used to moderate the effects of portion size on food consumption. One promising strategy is to reduce the energy density of foods, while maintaining food weight or volume, so that consumers can eat satisfying portions while reducing their energy intakes. There is a need for effective educational messages that not only emphasize limiting the consumption of foods high in energy density, but also encourage the consumption of those with a low energy density, such as fruits and vegetables. The delivery of consistent messages will require more cooperation among the food and restaurant industries, policy makers, and scientists. Effective strategies will also require consumers to understand and accept the importance of eating reasonable portions for better health.