Although the vast majority of diabetes cases (type 1 and type 2) are polygenic diseases, research, funded by the American Diabetes Association, has found that some forms of diabetes, distinct from type 1 or type 2 diabetes, are caused by single gene mutations. It has been estimated that these monogenic forms of diabetes account for up to five percent of all diabetes cases. In addition to monogenic diabetes, there are other atypical causes of diabetes, including: genetic defects in insulin action; diseases of the exocrine pancreas; and endocrinopathies. Given recent advances in our understanding of sub-types of diabetes, the time has come for a book on how to correctly diagnose and treat patients with atypical forms of this disorder. The book will be divided into three parts, each exploring distinct categories of atypical diabetes. Part I: Monogenic Diabetes: Genetic Defects of β-cell development and function; Part II: Insulin resistance, genetic defects in insulin action, and diseases of exocrine pancreas; Part III: Endocrinopathies, Immune-mediated diabetes, Diabetes of Unknown cause, and Other genetic syndromes sometimes associated with diabetes.