Two models for conceptualizing eating behavior are presented and the development of the experimental methodology to examine eating behavior is described in historical context. Specific studies of eating behavior in eating disorder patients are described with emphasis on how these studies examine aspects of the two hypothetical models that are presented on eating behavior. The studies present and focus on hunger and satiety perceptions, cognitive sets, and the neurotransmitter associated with satiety, serotonin. Unfortunately, no single investigation can encompass all of the variables that need to be measured that affect eating behavior. The studies described of both acutely ill and short-term recovered eating disorder patients indicate there may be some perceptual and physiological traits that are present in anorexia nervosa and bulimia nervosa. Studies over a longer period of time are needed to substantiate this. An eventual integrative explanation of disturbed eating behavior that is documented in eating disorder patients will be possible only after extensive investigations of the components.