Psychosomatic affection is defined as a bodily disorder whose nature can be appreciated only when emotional disturbances (i.e. psychological happenings) are investigated, in addition to physical disturbances (i.e. somatic happenings). Psychosomatic theory holds that emotional changes in human beings are accompanied by psychological changes and that if these emotional changes are persistent or frequent, then pathological physical factors can help to maintain or aggravate the disease, or to trigger relapses. It is also assumed that physical conditions induced in this way will improve if the psychological disturbance improves, either spontaneously or as a result of psychological treatment. This chapter covers the historical overview, classification, current status of psychosomatic theory, theoretical concepts and formulations, models of psychosomatic medicine, gastrointestinal disorders, cardiovascular system, musculoskeletal disorders, skin disorders, and endocrinal and metabolic disorders.