Claudins are a family of proteins that play a crucial role in forming tight junctions between cells. These tight junctions are essential for maintaining the integrity of epithelial and endothelial barriers, which control the passage of substances between different compartments in the body. By regulating permeability, claudins help protect tissues and organs from harmful substances and pathogens. There are over 20 different types of claudins, each with unique properties and functions. They are found in various tissues, including the intestines, kidneys, and blood-brain barrier. Research on claudins is important for understanding various diseases, including cancer and inflammatory disorders, as alterations in claudin expression can affect cell behavior and tissue function.