This book provides an updated account of tight junctions of different epithelia and endothelia and addresses their anatomy, biochemistry, physiology, synthesis, assembly, and modulation. It also discusses the relationship between molecular structure, function, regulation, posttranslational modifications of tight junction proteins and their role in gut microbiota maintenance, epithelial-mesenchymal transition, and intestinal barrier dysfunction-associated disorders important for the progression of human cancers. This book presents the pathological alterations of tight junctions at the blood-brain barrier that intensify or even initiate neurological dysfunction. Further, it reviews the significance of tight junctions and tight junction proteins in cancer development, infectious diseases, allergic reactions, and autoimmune disorders. Lastly, it highlights strategies for modulating tight junctions to enhance drug availability and organ deposition. This book is immensely useful for basic, translational, clinical, and interdisciplinary cancer researchers, practicing oncologists, and immunologists.