Publisher Summary This chapter discusses concepts related to insulin and the pancreas. The primary structure of insulin from a variety of species has been determined. All insulins so far studied consist of an acidic (A) and a basic (B) chain usually containing 21 and 30 amino acids, respectively. A large variety of substances are now known to affect “release” of insulin, including carbohydrates, sulfonylureas, amino acids, hormones, β-adrenergic agents and possibly lipids. “Release,” however, is not a single phenomenon, but is the result of many pancreatic processes. Sufficient evidence is available to show that some agents affecting release can differ in the pancreatic site on which they act. Efforts to find a common metabolic signal for release are complicated by the probability that the signals controlling various pancreatic steps may differ. Furthermore some agents, such as glucose, sulfonylureas, and leucine can act independently while most other “releasing” substances actually require the presence of one of the independent stimulators. In this chapter, chemical structure and activity of insulin is explained. The process of biosynthesis, storage, and secretion of insulin are elaborated. Metabolism of islet cells is also described.