The current renewed interest in the field of bipolar disorders can be attributed to various factors which are reviewed in this Special Section of the International Journal of Neuropsychopharmacology. Bipolar disorders are one of the most frequent disorders in psychiatry and this Special Section presents papers on recent advances in the clinical course, epidemiology, biological models and neurobiology of bipolar disorders. Novel therapeutic approaches will be covered in a second part in Volume 6, Number 3 (September 2003).