Complexes consisting of PDZ proteins have been implicated in a variety of cellular processes. In recent years, it has become increasingly clear that PDZ proteins play essential roles during the establishment of spatial asymmetry in various metazoan cell types such as epithelial cells. Epithelial cells possess asymmetry with respect to the apicobasal axis reflected by the differential distribution of proteins and lipids in the apical and basolateral surfaces. In Drosophila, three PDZ protein complexes have been shown to play crucial functions during the establishment of cell-cell adhesions and epithelial cell polarity: Bazooka/Dm-Par6/DaPKC, Crumbs/Stardust/Discs Lost, and Scribble/Discs Large/Lethal Giant Larvae. In this review, we focus primarily on our current knowledge of the localization and function of these complexes in Drosophila epithelia. We also discuss recent data that enhance our understanding of the homologous protein complexes and their roles during junctional assembly and polarization of mammalian epithelial cells.