Met is a high affinity receptor for hepatocyte growth factor (HGF; also known as scatter factor). Met is a disulfide-linked heterodimer made of 45kD alpha- and 145kD beta-subunits. The alpha-subunit and the amino-terminal region of beta-subunit form the extracellular domain. The remainder of the beta-chain spans the plasma membrane and contains a cytoplasmic region with tyrosine kinase activity. Interaction of Met with HGF results in autophosphorylation at multiple tyrosines, which recruit several downstream signaling components, including Gab1, c-Cbl and PI3 kinase. This is critical for all of its known biological functions. Phosphorylation of Tyr1234/1235 in the Met kinase domain is critical to kinase activation. Phosphorylation of Tyr1349 in the Met cytoplasmic domain provides a direct binding site for Gab1. Altered Met levels and/or tyrosine kinase activities were found in different tumors, especially in renal, colon and breast cancers. Met is an attractive therapeutic target and cancer diagnostic.