This paper proposes that the syndrome of mania rather than mood swings is the central distinguishing feature of bipolar disorder, which may be more appropriately viewed as manic disorder. The theoretical consequence of this change in perspective is to regard the depressive mood states as being a co-morbid condition. This may lead to a more profound and broader understanding of the variety of states of depression that complicate manic disorder. The paper also reviews diagnostic issues relating to bipolar depression. A broader approach may extend therapeutic choices, and open innovative research avenues.