The biological or medical approach views mental illness as if it were a disease or physical defect in the brain or body. Within the social approach, there are three dominant theories of mental illness etiology: stress theory, structural strain theory and labeling theory. This chapter describes each theory's basic concepts and assumptions, theoretical limitations and advantages, and implications for treating or preventing mental illness. According to stress theory, when events and strains accumulate in people's lives, they can overwhelm people's psychosocial resources and abilities to cope and then generate symptoms of psychological disorder. Labeling theory picks up at this point and suggests that frequent, severe, or highly visible symptoms or symptoms exhibited by those with little social prestige or power, can launch a victimizing process. Societal reactions to symptoms may result in the person's receiving a formal psychiatric diagnosis, becoming hospitalized, and, ultimately, accepting a mental patient identity.