Transitions between epithelial and mesenchymal cell phenotypes occur as part of normal organ development and wound healing, and are also observed in cancer, fibrosis and other diseases. Although the latter processes involve dysregulated interconversion of epithelial and mesenchymal cell phenotypes, the molecular mechanisms and sequences of cellular changes often closely resemble events that occur as a part of normal development and tissue repair. While primarily epithelial to mesenchymal transition (EMT) has been implicated in cancer and fibrosis, both EMT and mesenchymal to epithelial transition (MET) occur during organogenesis and development.