Focal adhesion kinase (FAK) is a non receptor protein tyrosine kinase discovered as a substrate for Src and as a key element of integrin signaling. FAK plays a central role in cell spreading, differentiation, migration, cell death and acceleration of the G1 to S phase transition of the cell cycle. FAK regulation includes phosphorylation at multiple tyrosine and serine residues. Phosphorylation of tyrosine generally is associated with positive regulation and growth promotion, however, dephosphorylation at these sites occurs as cells enter mitosis (M-Phase of the cell cycle). In contrast, serine phosphorylation either remains high or is increased as cells enter mitosis and may play a role in focal adhesion disassembly. FAK and its phosphorylation states have been implicated in cancer metastasis and tumor cell survival and adhesion-independent growth. Additionally, recent evidence indicates that elevation of FAK activity in human carcinoma cells is associated with increased invasive potential. A central role in tumor formation and progression suggests that FAK is an attractive target for therapeutic intervention.