There are various hotel rating systems used around the world, with most using a star system to categorize hotels based on facilities and quality. Systems can consider amenities, services, size, and facilities to determine a hotel's rating. Internationally, there is no single agreed-upon system, but Europe uses a system established by the European Hotelstars Union that rates hotels from one to five stars based on criteria within categories like rooms, services, and facilities. Other systems may use diamonds, environmental criteria, or religious standards in their ratings.