The importance of controlling energy balance in weight management is well established. Theoretically only a small daily adjustment in energy intake should, in time, yield significant weight loss. However, this small behavioural adjustment seems very difficult to sustain for most individuals trying to loose weight. Interventions are often developed on the assumption that appetite expression and eating behaviour in the overweight and obese functions similarly, all be it less effectively, as in the lean. Current evidence suggests there is no such thing as distinct obese eating style. However, a number of key behavioural traits are linked with over-consumption and obesity. On a basic level these include increased eating rate and meal size suggesting the obese experience deficits in within-meal satiation. However, a more complex cluster of behavioural traits such as a weakened satiety response to fatty meals, a preference for fat that is not diminished by satiety, a stronger hedonic attraction to palatable foods and to eating and higher trait hunger and disinhibition scores are all associated with adiposity. Over-responsiveness to external food cues may also be a key obesity promoting characteristic. Numerous mechanisms underlie appetite expression and recent evidence suggests that behavioural, rather then metabolic, differences mediate the genetic disposition to become obese. For instance variance at the FTO gene has been associated with over-consumption, reduced satiety responsiveness and possibly the enjoyment of food. Collectively, these data suggest that interventions which modify eating behaviour may be particularly important in the prevention and treatment of obesity.