Epithelial cells cover the outer and inner surfaces of the body, forming a selective polarized barrier between the intercellualar space and the external world. Linking the cells of this continuous layer and contributing to epithelial organization and function are specialized membrane domains--desmosomes, gap junctions, and occluding junctions. The contributors to this multidisciplinary symposium volume explore the nature of such junctional structures, focusing on the molecular organization and diversity of their constituent proteins, their formation and control, and interactions with ions and cytoskeletal elements. The physiological significance of cell-cell interaction in epithelia is considered, with reference to cell adhesion, barrier formation and intercellular communication, and to the functional implications for tissue architecture, embryonic development, morphogenesis and carcinogenesis.