"Addiction" used to remind anyone of the use or abuse of chemical substances. In recent years, however, researchers and clinicians have begun to classify other excessive behaviors including gambling, eating shopping and self-injury into the addictive behavior. Above all, pathological gambling and bulimia nervosa patients often make trouble for psychiatrists and psychologists, not only for their family. On the other hand, the neural substrata underlying substance dependence have been revealed. Especially, it is implicated that the mesolimbic neuron plays a crucial role on the reward system. The recent studies suggest that reduced activation of the reward system might be related to the addictive behaviors such as pathological gambling, binge eating and sexual behavior. Further biological researches about the addictive behavior would help our deeper understanding of its disorders. As to the pharmacotherapy, many studies have demonstrated the efficacy of selective serotonin reuptake inhibitors (SSRIs) in treating the addictive behaviors.