The protein product of c-met proto-oncogene, Met, is a tyrosine kinase receptor for the hepatocyte growth factor (HGF), also known as the scatter factor (SF). HGF/SF-Met signaling has multifunctional effects on mammalian cells. These include stimulation or inhibition of cellular proliferation, promotion of cell movement, invasion into extracellular matrix, and induction of glandular/tubular morphogenesis by epithelial cells. There is a substantial body of experimental evidence that supports the oncogenic role of HGF/SF-Met signaling pathways. This is putatively mediated by autocrine or paracrine mechanisms that promote tumor cell growth, invasion and angiogenesis. We review the evidence that HGF/SF and Met receptor play significant roles in the pathogenesis and biology of human cancers.