This chapter discusses goings-on in the stomach, where all the food that we eat is delivered to the stomach almost instantaneously. Gastric juice, which is acidic, is secreted by the stomach in anticipation of the arrival of food. Gastric juice initiates the digestion of proteins. The stomach has a richly glandular mucosa which is lined by simple columnar epithelium. Gastric secretion is accurately synchronized with the need for gastric juice. Hydrogen ions are actively secreted into the lumen. The potential difference persists even in the non-secreting stomach. The acid producing cells and pepsinogen producing cells respond to most of the regulatory factors in a similar way. Gastrin release is inhibited by somatostatin. Acetylcholine is released by the postganglionic parasympathetic fibres of the vagus nerve. Histamine is a very potent stimulator of gastric acid secretion. Somatostatin secretion is stimulated by gastric acidity. Proteins, fats and carbohydrates have a duodenal site of action.