Maturity Onset Diabetes of the Young is a particular form of type 2 diabetes, classically defined by an autosomal dominant inheritance, a young age at diagnosis (before 25 years) and an insulin secretion defect. At this time, six MODY genes have been described. Beyond the apparent simplicity, the study of such monogenic model of disease may help us to approach a complex disease such as type 2 diabetes, where is involved to conserve a genetic and environmental factors network. This different approach may help us to better understand type 2 diabetes physiopathology.