Psychiatric classification or psychiatric nosology is the classification and scientific study of mental disorders. For instance, the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) and the International Classification of Diseases, 11th edition (ICD-11) are widely used in the diagnosis and study of mental disorders. The DSM-5 is authored by the American Psychiatric Association while the ICD is authored by the World Health Organization (WHO).