Episodes of mania and melancholy have been recognized since Antiquity. They were attributed to black bile and considered as two distinct pathological states. From the xviiith century onwards, they were thought of as two aspects of the same illness. In the xxth century, “periodic insanity” characterized by thymus disorders were named by nosography as: “manic-depressive psychosis”. Later on, it was called: “bi-polar disorder”. At the beginning of the xxth century, the demonstration of the effectiveness of lithium salts (used in medicine ever since the xixth century), in the treatment of acute episodes and in the regulation of the thymus, led to create the notion of “bipolar mood disorder” and the description of their different forms. Early xxist Century nosography dissociates bipolar and unipolar disorders that only include depressive episodes.