Dr. Roger McIntyre, Professor of Psychiatry and Pharmacology at the University of Toronto and Head of the Mood Disorders Psychopharmacology Unit at the University Health Network in Toronto, Canada, introduces us to bipolar disorders. We discuss the key clinical features of bipolar disorders, the relationship between bipolar disorders and circadian rhythm, known pathogenesis, and some first line treatment options. We also contextualize the difference between "type I" and "type II" bipolar disorder, and explore the relationship between bipolar disorder and traumatic life experiences. For more: Bipolar Disorders (Lancet Seminar)