Integrins are transmembrane proteins that mediate interactions between adhesion molecules on adjacent cells and/or the extracellular matrix (ECM). They have diverse roles in several biological processes including cell migration during development and wound healing, cell differentiation, and apoptosis. Their activities can also regulate the metastatic and invasive potential of tumor cells. They exist as heterodimers consisting of alpha and beta subunits. Some alpha and beta subunits exhibit specificity for one another, and heterodimers often preferentially bind certain cell adhesion molecules, or constituents of the ECM. Although they themselves have no catalytic activity, integrins can be part of multimolecular signaling complexes known focal adhesions.