Fibronectin is an adhesive glycoprotein present in the extracellular matrix of embryogenic and adult tissue. These molecules primarily aid in regulating cell motility and attachment. A fibronectin molecule is composed of two identical polypeptide chains attached to each other by a pair of disulfide bonds at the C-terminal.

Both proteoglycans and collagen are attached to fibronectin proteins, which, in turn, are attached to integrin proteins. These integrin proteins interact with transmembrane proteins in the plasma membranes of eukaryotic cells that lack cell walls. In addition to associating with integrin, fibronectins also have an affinity for other host and non-host molecules.

Vertebrates have two types of fibronectins. The soluble plasma fibronectins found in blood plasma produced by hepatocytes are one type, and the other type is insoluble cellular fibronectin found in the extracellular matrix.

Fibronectin molecules also play an important role in blood clotting, as the plasma fibronectin is also deposited along with fibrin at the site of injury to stop bleeding. The plasma fibronectin is later digested by proteases secreted by fibroblasts. Further, the fibronectin produced by fibroblasts is insoluble and forms an insoluble matrix.