With the exception of inhaled oxygen, all of the atoms and molecules for building, maintaining, and powering the body normally have to be taken in by mouth. Food and beverages then have to be processed in the digestive tract to become useful. The various segments of the gastrointestinal tract cooperate to acquire and modify food, extract nutrients from it, and prepare the residue for excretion. This chapter goes into details of the anatomy, function, and specific interactions between the digestive organs. Molecular mechanisms of nutrient transport, renal processing, the blood–brain barrier (BBB), and materno-fetal nutrient transport all have large, devoted coverage.