The cloning of the insulin receptor not only established the primary structure of this membrane-bound glycoprotein but also offered the material necessary for the study of the molecular functions of this tyrosine-kinase receptor using molecular biology tools. This short review will summarize the actual knowledge of the structure, the functions (molecular structure of the binding site, tyrosine-kinase functions and role of autophosphorylation) and of the pathology of this receptor in extreme insulin resistances and type II diabetes.