Transitional epithelium also known as urothelium is a type of stratified epithelium. Transitional epithelium is a type of tissue that changes shape in response to stretching (stretchable epithelium). The transitional epithelium usually appears cuboidal when relaxed and squamous when stretched.

Due to its location in the excretory system, especially in the ureters and urinary bladder, one of the primary functions of this tissue is to be an extremely effective permeability barrier, impenetrable to water and most small molecules