The insulin receptor is a complex multifunctional protein located on the cell surface within the fluid mosaic matrix of the plasma membrane. Its ability to bind insulin is determined by structural and spatial specificity, high affinity and reversibility. Insulin action at the cellular level can be considered in three stages. The first stage includes the insulin receptor itself, the insulin substrate (IRS-1) and the molecules that interact with IRS-1. The second stage is that of cascade phosphorylation and dephosphorylation. The third stage concerns the final biological effects of the insulin cascade. The biological specificity of insulin binding and heterogeneity of insulin action in different cells has been well documented. This review intends to summarize the available data of structural and functional characteristics of insulin receptor.