Bipolar disorder is one of the most distinct syndromes in psychiatry. Bipolar I disorder affects approximately 1 percent of the population worldwide. About 50 percent of patients with bipolar illness have a family history of the disorder. Studies of twins suggest that the concordance rate of bipolar illness is between 40 percent and 80 percent in monozygotic twins. Although researchers have proposed myriad subtypes of depression, there are two major subtypes of disorder according to DSM-IV-TR: bipolar I and bipolar II. Bipolar I disorder is diagnosed on the basis of a single lifetime manic or mixed episode. Indeed, in one follow-up survey of tertiary care patients, depressive symptoms were more than three times as frequent as manic symptoms. Antidepressant monotherapy in an undiagnosed bipolar disorder patient can have devastating effects. So, clinical evaluation of a patient presenting with depression should always include the assessment for bipolar disorder. In addition to major episodes, it is important to pay attention to the course of subsyndromal and prodromal symptoms. Treatment options for bipolar disorder have rapidly expanded over the last decade. The literature supports the efficacy of a list of agents for the management of bipolar disorder, including lithium, valproate, lamotrigine, and carbamazepine, as well as the atypical antipsychotics olnazapine, risperidone, quetiapine, ziprasidone, and aripiprazole.