Fibronectin (Fn) is a large modular glycoprotein that is found as a polymeric fibrillar network in the extracellular matirx (ECM) and as soluble disulfide-linked dimeric protomers in plasma and other body fluids.

The protein subunit is made up of three types of homologous structural repeats termed Fn type I, type II, and type III repeats. Multiple isoforms of the protein formed by alternative splicing at numerous sites, resulting in insertions of extra type III domains (EDA and ECB) or parts of the variable type III connecting segment (V/IIICS), have been identified. Fibronectin is a ligand for fibrin, heparin, chondroitin sulfate, collagen/gelatin, and many integrin receptors. It is involved in multiple cellular processes including cell adhesion/migration, blood clotting, morphogenesis, tissue repair, and cell signaling.