Cortactin is a ubiquitous actin-binding protein that was originally identified as a substrate for Src. It is accumulated in peripheral, actin-enriched structures of cells, including lamellipodia and membrane ruffles, suggesting that cortactin facilitates actin network formation. Cortactin has four major domains of interest:the N-terminal acidic (NTA) and tandem repeats domains, and the C-terminal proline-rich and SH3 Domains. NTA associates with the Arp2/3 and WASP complex at F-actin branches. Cortactin is involved in promoting cell motility and invasion, including a critical role in invadopodia, actin rich-subcellular protrusions associated with degradation of the ECM by cancer cells. Cortactin is phosphorylated by src family kinases at Y421, Y466, and Y482 and S405 and S418 that are phosphorylated by Erk family kinases. May contribute to the organization of cell structure. The SH3 motif may function as a binding region to cytoskeleton. Tyrosine phosphorylation in transformed cells may contribute to cellular growth regulation and transformation.