In epithelial and endothelial cell layers tight junctions form selective apicolateral paracellular barriers separating luminal and extracellular spaces from the underlying tissues. Within the tight junctions the tetraspan transmembrane proteins occludin, claudins, and tricellulin form anastomosing strands of protein complexes, which interconnect opposing membranes of neighboring cells. Phosphorylation of tight junction components is critically involved in the regulation of tight junction assembly, maintenance, and function. This chapter compares occludin and tricellulin phosphorylation by the serine/threonine kinases CK2 and CK1.