Paradigm shift from classic antatomic theories to contemporary cell biological views of CAKUT. Ectopic budding of the ureter from the Wolffian duct is the first ontogenic misstep that leads to many—if not all—congenital anomalies of the kidney and urinary tract (CAKUT). The ectopia results in hypoplastic kidney, ectopia of ureterovesical orifice, urinary outflow obstruction and/or reflux. Studies in several mutant mouse models have verified that ectopic ureteric budding indeed precedes formation of CAKUT. Often, the genes involved in navigating ureteric budding to the correct site also regulate later ontogenic events of the kidney and urinary tract. The wide spectrum of CAKUT, for example, multicystic dysplastic kidney, megaureter and atretic ureter, portray the additional important functions of these same genes that are activated at multiple sites and stages during the normal morphogenesis of the kidney and urinary tract