In-utero the placenta is the primary organ responsible for neonatal homeostasis of fluid and electrolyte balance. With birth, this responsibility now transitions to the neonatal kidney. For successful transition to extrauterine renal physiology to occur maturation of neonatal glomerular filtration must occur, which is dependent on the development of renal blood flow. While these functions are decreased at birth, the term infant's kidneys are still able to manage homeostasis and are sufficient for growth and development. However, stressors can limit the adaptive properties of the neonatal kidney. This is especially important for those infants born before 34 weeks' gestation, when nephrogenesis is not yet complete. Knowledge of the changes in renal physiology is essential in caring for the neonate during transition. This article describes those changes.