In summary, glucose metabolism in the placenta and fetus is characterized by a fairly exact balance between exogenous glucose supply from the mother and placental and fetal glucose utilization (directly and as lactate produced from glucose). The rate of glucose utilization and its rate of oxidation are largely determined by the maternal glucose concentration and are mediated in part by insulin. Thus, glucose and insulin act together to substitute glucose oxidation for the oxidation of other energy substrates and to direct glucose carbon into glycogen, fat, and protein accretion. After birth, endogenous glucose production and dietary glucose intake (as glucose or as galactose) must account for the maintenance of glucose supply. In many cases, however, the balance among glucose intake, glucose production, and glucose utilization is inexact in the transition from intrauterine to extrauterine life, leading to both hypoglycemia and hyperglycemia. Basic measurements of the glucose production rate and the glucose utilization rate can be made now in the fetus as well as in the neonate, but the factors producing perturbations in glucose supply and utilization and in regulating the responses to these perturbations remain to be measured.