Activation of integrins in the extracellular matrix (ECM) of eukaryotic cells promotes the formation of membrane adhesion complexes, known as focal adhesions, which can include cytoskeletal proteins and protein tyrosine kinases, such as focal adhesion kinase (FAK). Phosphorylation events occurring within focal adhesions influence processes that include mitogenic signaling, cell survival, and cell motility. FAK is a 125 kDa non-receptor tyrosine kinase that is ubiquitously expressed and highly conserved between species. FAK is recruited by Integrin clusters and variably phosphorylated depending on the effector molecules present in the focal adhesion. Phosphorylation of Tyr 407 is mediated through Src family kinases. Phosphorylation of Tyr 861 may occur through Src kinases and can also occur during epithelialmesenchymal transdifferentiation (EMT) and cell migration.