This chapter discusses forensic psychiatry, a science that deals with the application of knowledge of psychiatry in the administration of justice. Delusion, hallucination, illusion, impulse, lucid interval, schizophrenia, mood disorders, neurotic and somatoform disorders, and mental retardation, is discussed in detail. Neurosis is when a patient suffers from emotional or intellectual disorders, but does not lose touch with reality. Organic mental disorders are associated with transient or permanent brain dysfunction and include those with demonstrable cerebral disease, which may be either primary brain pathology or secondary to systemic diseases. Schizophrenia is characterized by thought and speech disorders, thought blocking, disorders of perception, and disorders of motor behavior. Anxiety disorder is the commonest symptom and commonest disorder in psychiatry. Four patterns of drug use disorders include acute intoxication, dependence syndrome, withdrawal state, and harmful use.