Tatooine is a fictional desert planet that serves as the setting for many key scenes in the Star Wars saga.
Theatres - Movie
Lucasfilm also built an entire set a few kilometers North-West of Tozeur in the middle of the desert. This set acted as Mos Espa in Star Wars Episode I: The Phantom Menace. The buildings are still there and can be visited.
Links: en.wikipedia.org, virtualglobetrotting.com