This chapter speculates how innate vulnerabilities and acquired changes may allow varieties of abnormal eating behavior to occur. In man, the cortical, deliberative component plays a more dominant role. The function of this system includes choices, costs, learning and decision making. An imbalance between these three components may explain some of the clinical variation in eating behaviors. Glucose, insulin and other GI-related hormones modulate brain appetite systems by mechanisms involving both the hedonic and nutrostat systems. The role of dopamine (DA) as a key neurochemical in the hedonic system has been confirmed by several studies. Neuroimaging studies designed to interrogate reward function and dopamine pathways in obesity have led to fascinating findings. The chapter presents a model of brain function in eating disorders. Both obesity and the eating disorders are associated with abnormal functioning in regulatory control areas and in the hedonic systems.