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Nectins are a family of Ca2+-independent immunoglobulin-like cell-cell adhesion molecules consisting of four members, which homophilically and heterophilically trans-interact and cause cell-cell adhesion. Nectin-based cell-cell adhesion is involved in the formation of cadherin-based adherens junctions in epithelial cells and fibroblasts. The nectin-based cell-cell adhesion induces activation of Cdc42 and Rac small G proteins, which eventually regulate the formation of adherens junctions through reorganization of the actin cytoskeleton, gene expression through activation of a mitogen-activated protein kinase cascade, and cell polarization through cell polarity proteins. Five nectin-like molecules (necls), which have domain structures similar to those of nectins, have recently been identified and appear to play different roles from those of nectins. One of them, named necl-5, which does not homophilically trans-interact, but heterophilically trans-interacts with nectin-3, regulates cell migration and adhesion. In this article, the roles and modes of action of nectins and necls in cell adhesion, migration, and polarization are reviewed.