Underground casinos are illegal gambling establishments that operate outside of the regulatory framework of a jurisdiction. The term "underground" does not necessarily mean that these casinos are physically located underground, although some may be hidden in basements, back rooms, or other secretive locations.

Top selected casino companies worldwide in 2024, by revenue\n\n In 2024, MGM Resorts was the top-ranking casino company in terms of revenue. It generated a total of 13.13 billion U.S. dollars in 2024, its closest competitor being Caesars Entertainment with a revenue of 10.82 billion U.S. dollars in the same year.