Claudins are integral proteins of the TJ. Each epithelia in the organism expresses a unique set of claudins that determines the degree of sealing of the paracellular pathway and the ionic selectivity of the tissue. TJs are dynamic structures whose organization and composition change in response to alterations in the environment as well as under physiological and pathological conditions. Changes in claudin expression and subcellular distribution can be analyzed in western blot and immunofluorescence experiments, employing a wide array of available specific antibodies against claudins. In this chapter, we describe in detail protocols used for western blot and immunofluorescence detection of claudins in epithelial cell lines and in various tissue samples.