The core function of the human stomach is as an aid to digestion. The four key components of gastric digestive function are its function as a reservoir, acid secretion, enzyme secretion and its role in gastrointestinal motility. The reservoir capacity of the stomach allows it to increase its volume significantly while internal pressure increases only slightly. Acid secretion is a very important non-immunological defence against invading pathogens as well as being an important mechanism for vertebrates to have more complex diets. Stimulation of acid secretion involves the translocation of H+/K+-ATPases to the apical membrane of the parietal cell. The stomach is also an important endocrine organ producing an array of peptide hormones important for both enteric and non-enteric physiology including ghrelin and leptin. In addition to the reservoir function, the stomach also plays an important motility role as a pump, which anatomically is provided by the distal two thirds of the corpus, the antrum and the pylorus. This article examines those four functions and the role that they play in normal physiologic function and examines how they may play a role in pathologic states.