This chapter discusses dissociative disorders. In recent years, hysteria has stood out among medical concepts for the sheer volume of discussion among professional historians, philosophers, sociologists, feminists, literature specialists, and others. The word hysteria has been used in so many contexts that it no longer has any one meaning. These various contexts include the following as impulsive, uncontrolled behavior (impulse dyscontrol), manipulative, dramatic, exhibitionistic, emotional and/or seductive behavior (histrionic or hysterical personality traits), absence of objective signs of an organic illness, and hypochondriasis. This chapter covers the historical perspective and the concepts of dissociation and conversion, epidemiology of dissociative disorder, classifications of dissociative disorders, clinical features of dissociative disorders, differential diagnosis of dissociative amnesia, and diagnosis of dissociative disorders.