The Diagnostic and Statistical Manual of Mental Disorders is the most widely accepted diagnostic system in the United States. First published by the American Psychaiatric Association (APA) in 1952, the DSM is used by medical professionals, insurance companies, and the court system to diagnose and define mental illnesses and disorders, including substance abuse and dependence. In fact, the diagnosis code assigned to a case often determines insurance reimbursement for treatment. The book is also an important indicator of societal mores: until 1973 homosexuality was defined as a mental disorder.

The first tabulation of mental illness in the United States appeared in the 1840 census, when the category "idiots" and the category "insane" were first counted. By the 1880 census, seven types of mental illness were recognized, including epilepsy. In 1917 the American Medico-Psychological Association (now the APA), in conjunction with the National Commission on Mental...