A comprehensive account of the role of the islets of Langerhans is presented in this text. As the primary source of hormone production in the pancreas, the islets of Langerhans have been the focus of research into the nature of diabetes for decades. In recent years, the molecular biology of this multiendocrine organ has been intensively investigated, with a corresponding increase in our understanding of the normal and pathological functioning of islet cells. This is the first comprehensive treatment of molecular studies on the synthesis of insulin, glucagon, somatostatin and pancreatic polypeptide. In addition, this volume presents contemporary hypotheses and explanations, at the molecular level, of the defects in islet cells that may lead to diabetes.