A Certain Magical Index (とある魔術の禁書目録インデックス Toaru Majutsu no Indekkusu) is a Japanese light novel series written by Kazuma Kamachi and illustrated by Kiyotaka Haimura, which has been published by ASCII Media Works under their Dengeki Bunko imprint since April 2004. The plot is set in a world where supernatural abilities exist. The light novels focus on Tōma Kamijō, a young high school student in Academy City who has an unusual ability, as he encounters an English nun named Index. His ability and relationship with Index proves dangerous to other magicians and espers who want to discover the secrets behind him, Index as well as the city.
Yen Press have licensed the novels in North America. A manga adaptation by Chuya Kogino began serialization in Monthly Shōnen Gangan from May 2007. J.C.Staff produced two 24-episode anime series between 2008 and 2011. An animated film was released in February 2013. The anime adaptations are licensed in North America by Funimation. A 26-episode third season aired between 2018 and 2019, licensed by Funimation. The side-story manga series, A Certain Scientific Railgun, began serialization in Dengeki Daioh in February 2007. A second side-story manga series, A Certain Scientific Accelerator, began serialization in Dengeki Daioh in December 2013.
The story is set in Academy City (学園都市 Gakuen Toshi), a technologically advanced city located in west of Tokyo that is known for its educational and research institutions. Tōma Kamijō is a student in Academy City whose right hand, the Imagine Breaker, has the ability to negate any supernatural power, but also negates his own luck, much to his chagrin. One day, Tōma meets a young English girl named Index – a nun from Necessarius, a secret magic branch of the Church of England, whose mind has been implanted with the Index Librorum Prohibitorum – 103,000 forbidden magical books that the Church has stored in secret locations. His encounter with her leads him to meet others from the secret worlds of science and magic. Tōma's unusual power places him at the center of conflicts between the Magicians and Espers in Academy City who try to unravel the secrets behind Academy City, Index, and Tōma's own special power.
Besides its own manga adaptation, the series also has two manga series which are side stories focusing on other main characters. One of them is A Certain Scientific Railgun, which focuses on Mikoto Misaka, an Electromaster and one of the most powerful Espers in the city. The second, A Certain Scientific Accelerator, focuses on Accelerator, a teenager who can control vectors, known as the most powerful Esper in Academy City.