Bipolar disorder, also known as manic depression, is a psychiatric illness characterized by recurrent manic/hypomanic and/or depressive mood episodes that cause significant impairment in functioning. Bipolar disorder can originate before the age of 18 years and is a chronic condition that [Page 198]continues across the lifespan. This entry describes the history of the modern-day disorder, defines manic and depressive episodes, presents clinical features of and associated with the disorder, defines how a diagnosis of bipolar disorder is made in adults and children, and identifies psychopharmacological and psychosocial interventions that are efficacious in the treatment of bipolar disorder.