The developing intestine is a complex organ that is responsible for absorption of nutrients, water and ions that are used either as a source of energy or are accumulated in the growing organism. This review describes the developmental profiles of ion transport at the organ level as well as the mechanisms that have been identified for mediating these transports. Information from studies of the developing intestine are integrated to derive a picture of maturation of transport functions. The maturation of intestinal structure and transport is not terminated at the time of birth. The transition from intrauterine parenteral nutrition to extrauterine enteral nutrition and later from maternal milk to solid food requires changes not only in morphology, but also in transport functions. The available data indicate that the development of intestinal transport represents the sequence of quantitative and qualitative changes resulting in a complete spectrum of nutrition, water and ion requirements of the growing
organism.