Bipolar disorder, also known as bipolar affective disorder, manic-depressive disorder, or manic depression, is a mental illness characterized by episodes of an elevated mood known as mania, usually alternating with episodes of depression.

During mania an individual feels abnormally happy, energetic, or irritable, but often makes poor decisions due to unrealistic ideas or poor regard of consequences. Manic and depressive episodes can impair the individual's ability to function in ordinary life.