Nectins are adhesion molecules that participate in the organization of epithelial and endothelial junctions and serve as receptors for herpes simplex virus entry. They belong to the immunoglobulin superfamily, are homologues of the poliovirus receptor (PVR/CD155), and were also named poliovirus receptor-related (PRR) proteins. We identify a new member of the nectin family named nectin4. Peptide sequences of human and murine nectin4 share 92% identity, and as for other members, the ectodomain is made of three immunoglobulin-like domains of V, C, C types. In contrast to other nectin molecules, detection of nectin4 transcripts is mainly restricted to placenta in human tissues. Expression is broader in mouse, and interestingly nectin4 is detected at days 11, 15, and 17 during murine embryogenesis. Nectin4 interacts with afadin, a F-actin-associated molecule, via its carboxyl-terminal cytoplasmic sequence. Both molecules co-localize at cadherin-based adherens junctions in the MDCKII epithelial cell line. Nectins are homophilic adhesion molecules, and recently heterophilic interactions have been described between nectin3/nectin1 and nectin3/nectin2. We confirmed these trans-interactions and also described nectin3 as the PVR/CD155 ligand. By means of several approaches, we report on the identification of nectin4 as a new ligand for nectin1. First, a soluble chimeric recombinant nectin4 ectodomain (nectin4-Fc) trans-interacts with cells expressing nectin1 but not with cells expressing nectin2, nectin3, or PVR/CD155. Conversely, nectin1-Fc binds to cells expressing nectin4. Second, nectin1-Fc precipitates nectin4 expressed in COS cells. Third, reciprocal in vitro physical interactions were detected between nectin4-Fc and nectin1-Fc. The nectin4-Fc/nectin4-Fc interaction was detected suggesting that nectin4 exhibits both homophilic and heterophilic properties. Using the same approaches we demonstrate, for the first time, that the V domain of nectin1 acts as a major functional region involved in trans-heterointeraction with nectin4 and also nectin3.