The document defines and describes Bipolar I disorder and related diagnoses. Bipolar I involves distinct periods of abnormally elevated or irritable moods lasting at least one week, along with other symptoms. It affects about 0.6% of the US population and typically begins manifesting in episodes around age 18, with over 90% of those with a single manic episode experiencing recurrences. The course often involves manic episodes preceding depressive ones, with some experiencing four or more mood episodes within a year (rapid cycling specifier).