The cadherin superfamily comprises over forty proteins which are ~50-60% homologous. Cadherin expression is required for the assembly of cells into solid tissues and importantly, cadherins are expressed in a tissue specific fashion. Homotypic cellular interactions are promoted by homophillic interactions between the extracellular regions of like cadherin molecules on neighboring cells. Recent crystal structure analysis of an extracellular cadherin domain suggests that individual cadherin molecules cooperate to form a linear cell adhesion zipper. In addition to playing important roles in differentiation and tissue morphogenesis, cadherins also appear to play a significant role in modulating tumor invasion and metastasis. The expression of E-cadherin correlates inversely with the motile and invasive behavior of tumor cells.