Temperament has been defined as the heritable biologically determined core of personality that remains stable throughout the life span and establishes the baseline level of reactivity, mood, and energy of a person. If the link between temperament and mental disorder goes back to the Greco-Roman medicine, Kraepelin was among the first authors to pay attention to the temperamental bases of bipolar disorder. He proposed four temperamental types that he described in the premorbid histories of the majority of manic-depressive patients, and found overrepresented in the biologic relatives of these patients. Building on this ancestry, Akiskal formulated the modern concept of affective temperament, and described five temperaments: depressive, hyperthymic, cyclothymic, irritable, and anxious. According to Akiskal's model, bipolar disorder lies along a continuum from temperament to full-blown episodes of affective illness. A series of recent studies have shown the role played by temperaments in the outbreak of bipolar episodes, their clinical presentation, as well as the illness course and comorbidities. Furthermore modern familial and genetic studies have confirmed the first observations of Kraepelin. It has been recently proposed that affective temperaments may carry distinct evolutionary advantages on the individual or a group level, so that affective disorders would be genetic reservoirs for adaptative temperaments and the price to be paid for the chance of exceptionality. Apart from these theoretical perspectives, paying attention to temperamental components may have important implications for the treatment of bipolar disorder. Finally recent studies confirmed as well, that the concept of affective temperament fulfilled the criteria required to be considered as an endophenotype.