Epithelial mesenchymal transition (EMT) is an important biological process enabling the malignant tumors of epithelial cell origin to acquire migratory and invasive ability. Among the mechanisms contributing to EMT, transforming growth factor β (TGF-β) is considered to play a key role. This paper overviews the relationship between EMT and tumor invasion and metastasis, and mentions the related signaling pathways mediated by TGF-β, which are responsible for EMT.