Claudin-6 (CLDN6) belongs to the claudins family and is a transmembrane protein found in tight junctions with two extracellular loops and intracellular N and C tails. CLDN6 modulates the ion- and charge-specific permeability of the paracellular pathway in most epithelial tissues. It regulates the paracellular flux of cations in the kidney through forming heterotypic strands with other claudins and has a role in maintaining the lung epithelial barrier function. The CLDN6 gene is adjacent to another family member, CLDN9, on chromosome 16. Certain CLDN6-positive cancers, encompassing ovarian, endometrial, and testicular malignancies, have been shown to have their proliferation and invasiveness suppressed upon CLDN6 silencing.