There have been significant advances recently in the understanding of the molecular causes of nephrogenic diabetes insipidus. The resistance of the collecting duct to the action of vasopressin in this disorder results from abnormalities in several of the intricate steps that mediate the increase in principal cell hydraulic conductivity in response to the hormone. In this article, we review the current understanding of the known genetic causes of nephrogenic diabetes insipidus that affect the binding of vasopressin to the V2 receptor and subsequent intracellular signaling events, as well as the translocation of aquaporin-2 water channels to the apical membrane. In addition, genetic diseases, which decrease collecting-duct water absorption by diminishing the interstitial medullary osmolarity, are discussed.