Depressive phases are the most prevalent component of bipolar disorders, even with modern treatment. Bipolar depressive morbidity is often misdiagnosed and is limited in response to available treatments. These conditions are especially debilitating and are associated with psychiatric comorbidity, substance abuse, functional disability, and increased mortality owing to early suicide and accidents, and later medical illnesses. There is growing awareness that bipolar depression is one of the greatest challenges in modern psychiatry. It is essential to differentiate various forms of depression, dysthymia, and dysphoric mixed states of bipolar disorders from the clinical features of more common, unipolar major depressive disorders. In bipolar depression, antidepressant responses often are unsatisfactory, and these agents probably are overused. Emerging treatments, including several anticonvulsant and modern antipsychotic drugs, as well as lithium—alone or in selected combinations—are partially effective for bipolar depression. Interest in recognizing bipolar depression and seeking more effective, specific, and safer treatments for it are growing.