MODY diabetes, for Maturity Onset Diabetes of the Young, is a form of monogenic diabetes characterized by a typical onset before the age of 25 years, the lack of autoimmunity against the b cells of the pancreas, a preserved β cells function and an autosomal dominant mode of inheritance. This type of diabetes constitutes 2 to 5% of all cases of diabetes but remains often undiagnosed. Nearly 15 MODY subtypes have been identified to date. The 3 most common subtypes are caused by mutations in the genes encoding glucokinase, HNF1a and HNF4a, and account for approximately 80% of all MODY cases. Carrying out a genetic test can thus make it possible to make the diagnosis of MODY diabetes and to set up an appropriate treatment. In this article we will discuss these 3 main MODY sub-type, although there are other forms, which may be characterized by associated specific organ damage.