Academy City is a landlocked sovereign city-state whose territory consists of a walled enclave within Western Tokyo. It is the primary setting of the Toaru Majutsu no Index series and its side stories.
As the city's name suggests, it is a city of several schools and institutions of higher learning from kindergarten to university level that learn side-by-side along with the scientists who research on psychic powers and higher technology, the latter being one of the primary reasons for its establishment. It is the most advanced city in the world and its technology is said to be 20 or 30 years ahead of the world. Academy City is composed of 23 districts, called School Districts which are simply numbered from one to twenty-three and each of these districts have a specific purpose.
In the novel series, there are only a handful of residents who know about magic, either due to encountering it or being part of the magic side themselves, such as Kamijou Touma, Index, Misaka Mikoto, Accelerator, and Hamazura Shiage.