In this monograph the authors have emphasized a number of important concepts in mammalian kidney development. Emphasis has been put on methodology so that the reader can understand how certain results or conclusions were reached and what the optimal methods for reliable results to be obtained are. In addition, as well as descriptions of the morphology there is information on the genetic basis of the structural development. In addition much attention has been paid to how nephron number may be altered by changes in the environment of the developing kidney and to the consequences for the remaining nephron gene expression and kidney function when total nephron number is altered. The consequences for the health of the adult, upon the formation of an adult kidney with altered nephron number and (potentially) gene expression, can be quite serious. The epigenetic mechanisms by which such changes can occur are introduced as a very fertile field for future investigation.