This work is intended to be a resource for both researchers in the field as well as endocrinologists, diabetologists, and geneticists who seek to learn more about this rapidly changing and important field. The text contains chapters from experts in the area who review aspects of the genetics of both type 1 and 2 diabetes mellitus as well as various syndromic forms of diabetes. The chapters are approachable for those who are not experts in the field of genetics but also comprehensive, so as to serve as an important resource for researchers interested in the genetics of diabetes mellitus. A description of basic concepts of the genetics of complex diseases like type 1 and type 2 diabetes is provided as background. Type 1 diabetes is addressed in chapters exploring genetic determinants that affect the autoimmune process characterisic of type 1 diabetes, the role of the insulin gene in the pathogenesis of type 1 diabetes and additional genes that may impact upon the risk of type 1 diabetes. The impact of genetic determinants on the pathophysiology of type 2 diabetes is covered, as are chapters that address specific genes that are important for the development of type 2 diabetes. Finally, syndromic forms of diabetes, including maturity onset diabetes of the young and mitochondrial diabetes, and the insight that these disorders provide into more common forms of diabetes are reviewed. Thus, this comprehensive text should serve as an important resource for those actively engaged in research in this area or clinicians treating these patients and for those needing an up-to-date entree to become more knowledgeable in the area.