Fibronectin is an ubiquitous glycoprotein that plays an important role in many biological processes. Plasma and cellular fibronectins are similar, but not identical molecular structures. Cellular fibronectin has ED1 and ED2 components that do no exist in plasma fibronectin. Human plasma fibronectin is a high molecular weight (440-530 kD) glycoprotein, consisting of two nearly identical subunits disulfide-bridged close to their C-terminal ends. Tetrapeptide "RGDS" and polypeptide "CS1" are receptors for cell surface integrins. Numerous receptors for macromolecules enable to bridging of fibronectin to the fibrin, heparin, factor XIIIa, plasminogen, tissue type plasminogen activator, collagen, bacterial and virus glycoproteins. Cellular fibronectin is a component of the fibrillar extracellular matrix compartment and basal membrane of all tissues that are involved in the tissue modelling in embryogenesis and tissue remodelling in wound healing. Plasma fibronectin is involved in the mechanisms of immune defence, immune surveillance and hemostasis.