The transition from benign tumors to invasive, metastatic cancer cells involves changes in the extracellular matrix environment, cell motility, and cell-cell adhesion. Because cell-cell–adhesion molecules are dynamically regulated during human carcinogenesis, they have been implicated in tumorigenesis, especially during the later stages of tumor progression—that is, tumor-cell invasion and metastasis (Thiery 1996). In this review, we focus on the evidence from genetics and cell-culture studies that support a functional role of E-cadherin/catenin adhesion complexes in carcinogenesis.