tight junctions between epithelial and endothelial cells form selective barriers and paracellular channels and regulate paracellular transport of solutes, immune cells, and drugs. the main goal of current tight junction research is to clarify the relation between molecular basis and physiological and pathological function. tight junctions consist of proteins that interconnect laterally neighboring cells of epithelia and endothelia. some kinds of these proteins seal the tight junction, so that a nearly impermeable barrier develops, others even form channels, which allow for permeation between the cells. the tight junction proteins of the claudin family (claudin-1 to -27 in humans) and the newly defined group of tamp (3 proteins: occludin, marvel-d2, and tricellulin) are characterised by four transmembrane domains and two extracellular loops. main topics of the volume are the functions of distinct tight junction proteins as barrier or channel formers for solutes and water, characteristics of the tight junction in inflammatory bowel diseases, posttranslational modifications of tight junction proteins, the relation between renal tight junction proteins and blood pressure control, and the molecular structure of claudin-claudin interactions