The heterotrimeric PDZ complex containing LIN‐2, LIN‐7 and LIN‐10 is known to be involved in the organization of epithelial and neuronal junctions in Caenorhabditis elegans and mammals. We report here that mammalian LIN‐7 PDZ proteins form a complex with cadherin and β‐catenin in epithelia and neurons. The association of LIN‐7 with cadherin and β‐catenin is Ca 2+ dependent and is mediated by the direct binding of LIN‐7 to the C‐terminal PDZ target sequence of β‐catenin, as demonstrated by means of co‐immunoprecipitation experiments and in vitro binding assays with the recombinant glutathione S‐transferase: LIN‐7A. The presence of β‐catenin at the junction is required in order to relocate LIN‐7 from the cytosol to cadherin‐mediated adhesions, thus indicating that LIN‐7 junctional recruitment is β‐catenin dependent and that one functional role of the binding is to localize LIN‐7. Moreover, when LIN‐7 is present at the β‐catenin‐containing junctions, it determines the accumulation of binding partners, thus suggesting the mechanism by which β‐catenin mediates the organization of the junctional domain.