Bipolar disorder is not a single disorder, but a category of mood disorders defined by the presence of one or more episodes of abnormally elevated mood, clinically referred to as mania. Individuals who experience manic episodes also commonly experience depressive episodes or symptoms, or mixed episodes which present with features of both mania and depression. These episodes are normally separated by periods of normal mood, but in some patients, depression and mania may rapidly alternate, known as rapid cycling. The disorder has been subdivided into bipolar I, bipolar II and cyclothymia based on the type and severity of mood episodes experienced.

Also called bipolar affective disorder until recently, the current name is of fairly recent origin and refers to the cycling between high and low episodes; it has replaced the older term manic-depressive illness coined by Emil Kraepelin (1856-1926) in the late nineteenth century. The new term is designed to be neutral, to avoid the stigma in the non-mental health community that comes from conflating "manic" and "depression."

Onset of symptoms generally occurs in young adulthood. Diagnosis is based on the person's self-reported experiences, as well as observed behavior. Episodes of illness are associated with distress and disruption, and a relatively high risk of suicide. Studies suggest that genetics, early environment, neurobiology, and psychological and social processes are important contributory factors. Psychiatric research is focused on the role of neurobiology, but a clear organic cause has not been found. Bipolar disorder is usually treated with medications and/or therapy or counseling. The mainstay of medication are a number of drugs termed 'mood stabilizers', in particular lithium and sodium valproate; these are a group of unrelated medications used to prevent relapses of further episodes. Antipsychotic medications, sometimes called neuroleptics, in particular olanzapine, are used in the treatment of manic episodes and in maintenance. The benefits of using antidepressants in depressive episodes is unclear. In serious cases where there is risk to self and others involuntary hospitalization may be necessary; these generally involve severe manic episodes with dangerous behaviour or depressive episodes with suicidal ideation. Hospital stays are less frequent and for shorter periods than they were in previous years.

Some studies have suggested a significant correlation between creativity and bipolar disorder. However, the relationship between the disorder and creativity is still very unclear. Santosa et al. Enhanced creativity in bipolar disorder patients: A controlled study. J Affect Disord. 2006 23 November; PMID 17126406. Rihmer et al. Creativity and mental illness. Psychiatr Hung. 2006;21(4):288-94. PMID 17170470. Nowakowska et al. Temperamental commonalities and differences in euthymic mood disorder patients, creative controls, and healthy controls. J Affect Disord. 2005 Mar;85(1-2):207-15. PMID 15780691. One study indicated increased striving for, and sometimes attaining, goals and achievements. While the disorder affects people differently, individuals with bipolar disorder tend to be much more outgoing and daring than individuals without bipolar disorder. The disorder is also found in a large number of people involved in the arts. It is an ongoing study as to why many creative geniuses had bipolar disorder.