In psychiatry, as in the rest of the medicine, Classification of Psychiatric Disorders is needed for three main purposes:
1. To enable clinicians to communicate with one another about their patients symptoms, prognosis and treatment.
2. To ensure that research can be conducted with comparable groups of patients.
3. To enable epidemiological studies as a basis for research and planning services.
Systems of classification: There are mainly two systems of classification which are described in brief below.