Bipolar depressions can present all the clinical aspects from a major depressive episode with a mild intensity to severe one. However, part of this severity comes from the bipolarity by itself. Bipolar disorders belong to the 10 most disabling conditions in the world. Moreover, the complexity of bipolar depressions comes also from the complexity to treat them. Antidepressants are difficult to use in bipolar subjects because the risk of switch, the possible induction of rapid cycles or of a chronic dysphoric state. Currently, guidelines are not very helpful for the choice of the treatment in case of an acute major depressive disorder. Indeed, the current guidelines give the choice between a mood stabilizer alone or associated with an antidepressant, either between an antipsychotic more or less associated with an antidepressant. A better understanding of the clinical heterogeneity of bipolar depression could help to solve a part of this complexity.