Epithelial-mesenchymal transition (EMT) is a biological process where epithelial cells lose their polarity and acquire mesenchymal traits, enabling migration, invasion, and ECM production. EMT occurs in three distinct contexts: type 1 during implantation, embryogenesis, and organ development; type 2 during tissue regeneration and fibrosis; and type 3 in cancer progression and metastasis. Type 1 EMT generates mesenchymal cells that can later undergo mesenchymal-epithelial transition (MET) to form secondary epithelia. Type 2 EMT is associated with inflammation and fibrosis, leading to organ damage if not resolved. Type 3 EMT is linked to cancer, where cells acquire a mesenchymal phenotype to invade and metastasize. EMT is driven by various signaling pathways, including Wnt, TGF-β, and FGF, and involves transcription factors like Snail, Slug, and Twist. EMT is reversible, with MET allowing cells to return to an epithelial state. EMT plays a critical role in development, tissue repair, and disease, with implications for therapeutic interventions. Understanding the molecular mechanisms of EMT is essential for developing strategies to prevent or treat fibrosis and cancer.Epithelial-mesenchymal transition (EMT) is a biological process where epithelial cells lose their polarity and acquire mesenchymal traits, enabling migration, invasion, and ECM production. EMT occurs in three distinct contexts: type 1 during implantation, embryogenesis, and organ development; type 2 during tissue regeneration and fibrosis; and type 3 in cancer progression and metastasis. Type 1 EMT generates mesenchymal cells that can later undergo mesenchymal-epithelial transition (MET) to form secondary epithelia. Type 2 EMT is associated with inflammation and fibrosis, leading to organ damage if not resolved. Type 3 EMT is linked to cancer, where cells acquire a mesenchymal phenotype to invade and metastasize. EMT is driven by various signaling pathways, including Wnt, TGF-β, and FGF, and involves transcription factors like Snail, Slug, and Twist. EMT is reversible, with MET allowing cells to return to an epithelial state. EMT plays a critical role in development, tissue repair, and disease, with implications for therapeutic interventions. Understanding the molecular mechanisms of EMT is essential for developing strategies to prevent or treat fibrosis and cancer.