A Certain Magical Index is a Japanese light novel series written by Kazuma Kamachi and illustrated by Kiyotaka Haimura. The series follows Tōma Kamijō, a high school student in the scientifically-advanced Academy City, who meets a young nun named Index from the Church of England whose mind has been implanted with the Index Librorum Prohibitorum: the magical texts which the church removed from circulation. His encounter with her leads him to meet others from the secret world of science and magic and into an adventure with his friends where science and magic collide.
ASCII Media Works published 24 volumes under their Dengeki Bunko imprint between April 10, 2004 and October 10, 2010. Two of the 24 novels are short story compilations released in July 2007 and November 2008. The first volume of a sequel series titled New Testament: Toaru Majutsu no Index was published on March 10, 2011. Yen Press have licensed the series in North America and began releasing it under their Yen On imprint in November 2014. Toaru Majutsu no Index became Dengeki Bunko's No. 1 bestseller in May 2010, and in August 2010, it was reported that the novels had sold 9 million copies and became the fifth best selling light novel in Japan.
A Certain Magical Index was adapted as a 24-episode anime television series by J.C.Staff, which aired in Japan between October 2008 and March 2009, covering the events of the first six novels. A second season of A Certain Magical Index aired between October 2010 and March 2011, titled A Certain Magical Index II.