The light novels focus on Toma Kamijo, a young high school student in Academy City with the ability to cancel other espers' powers, as he encounters an English nun named Index.

He got the chance to write a full series and decided to create it with the concept of exploring the rules of magic, rather than just having it exist, and the inclusion of science to oppose its elements.

The story is set in Academy City (学園都市, Gakuen Toshi), a technologically advanced independent city-state located in the west of Tokyo, Japan, which is known for its educational and research institutions.

The fourth, A Certain Scientific Mental Out, follows the fifth Level 5 Esper and most powerful psychological psychic named Misaki Shokuhō in her election campaign for the next president of Tokiwadai Middle School's student body.

[5] He avoided using difficult kanji for Toma Kamijo's name to help readers able to read it but he kept the meaning behind the character's epithet ("The One Who Purifies God and Slays Demons") a secret for now.

[5] When it came the time to write the story, Kamachi investigated the terms "sorcerer" and "real" online for him to build the world of magic and the magicians' existence in his light novel.

This helped him to create the idea of Toma Kamijo's known power, the Imagine Breaker, and set the stage for the world-building of Academy City "where science, espers, and magic would gather".

[15] A third light novel series, titled A Certain Magical Index: Genesis Testament (創約 とある魔術の禁書目録, Sōyaku Toaru Majutsu no Indekkusu), began publication on February 7, 2020.

The first short novel, titled A Certain Magical Index SS: Love Letter Competition, was included in the release of Kiyotaka Haimura Artbook rainbow spectrum:colors on February 28, 2011.

[22] The second short novel, titled New Testament: A Certain Magical Index SS, was included in the release of Kiyotaka Haimura Artbook 2 rainbow spectrum:notes on September 9, 2014.

[23] The third short novel, titled Genesis Testament: A Certain Magical Index SS, was included in the release of Kiyotaka Haimura Artbook 3 CROSS on May 9, 2020.

[24] The bonus novels that Kamachi wrote for the series' Blu-ray/DVD releases are compiled into two volumes titled A Certain Magical Index: Apocrypha Archive (とある魔術の禁書目録 外典書庫, Toaru Majutsu no Indekkusu: Gaiten Shoku) to commemorate the 15th anniversary of his debut,[25] which were published on June 10[26] and August 7, 2020.

[36] A side-story manga series illustrated by Motoi Fuyukawa, titled A Certain Scientific Railgun, started serialization in the April 2007 issue of Dengeki Daioh.

[44] A third side-story manga series illustrated by Nankyoku Kisaragi, titled A Certain Scientific Dark Matter (とある科学の未元物質, Toaru Kagaku no Dāku Matā),[c] was serialized in ASCII Media Works magazine Dengeki Daioh from August 27, 2019, to March 26, 2020 (the same day the compiled volume was published).

[45] A fourth side-story manga series illustrated by Yasuhito Nogi, titled A Certain Scientific Mental Out (とある科学の心理掌握, Toaru Kagaku no Mentaru Auto),[d] began serialization in Comic Newtype website on July 27, 2021.

[47] A yonkoma manga spin-off illustrated by Mijin Kouka, titled A Certain Everyday Index-san (とある日常のいんでっくすさん, Toaru Nichijō no Indekkusu-san), was serialized in Square Enix's Monthly Shōnen Gangan magazine from September 12, 2013,[48] to May 12, 2016.

[51] In March 2023, Kamachi revealed the manga adaptation of A Certain ITEM of Dark Side by Strelka which is serialized in Dengeki Daioh magazine[52][53] starting October 26 of that year.

[61] An animated film titled A Certain Magical Index: The Movie – The Miracle of Endymion (劇場版 とある魔術の禁書目録 エンデュミオンの奇蹟, Gekijōban Toaru Majutsu no Indekkusu: Endyumion no Kiseki) was released in Japan on February 23, 2013.

[93][94] The first ending theme music is "Eve of a Revolution" (革命前夜, Kakumei Zenya), while the second one is "The Never-Ending Song" (終わらない歌, Owaranai Uta), both performed by Yuka Iguchi.

[93][94] A 3D fighting game titled A Certain Magical Index was developed by Shade for the PlayStation Portable (PSP) and published by ASCII Media Works on January 27, 2011.

[95][96] Heroz developed a social card game for Mobage titled A Certain Magical Index: Struggle Battle, which was published by ASCII Media Works on December 25, 2012.

[110] A radio drama was broadcast in Dengeki Taishō, narrating the story of an encounter with the mysterious self-proclaimed "former" sorcerer by Toma Kamijo and Index in a family restaurant after Mikoto Misaka decided to go back due to urgent business.

[112] The drama CD, which contains a new story about Misaka and Kuroko Shirai with their "urgent business" and a duel request by a Level 3 psychic girl from Tokiwadai Middle School, became available for purchase in December 2007.

[116] A drama CD for A Certain Magical Index III was released as a bonus for customers who purchased the limited edition volume sets of the series via Amazon's Japanese website.

[118] As a collaboration with Sega's Virtual On video game franchise, Kamachi wrote the crossover light novel titled A Certain Magical Index × Cyber Troopers Virtual-On: A Certain Magical Virtual-On (とある魔術の禁書目録×電脳戦機バーチャロン とある魔術の電脳戦機, Toaru Majutsu no Indekkusu × Den'nō Senki Bācharon: Toaru Majutsu no Bācharon) with mecha illustrations designed by Hajime Katoki, which was released on May 10, 2016.

[120] A manga adaptation of The Circumstance Leading to a Simple Killer Princess' Marriage Was a Certain Magical Heavy Zashiki Warashi was serialized on Monthly Shōnen Gangan from February 12[121] to October 10, 2015.

[124] A manga adaptation of A Certain Magical Virtual-On began publication in ASCII Media Works' Monthly Denplay Comic magazine from March 10, 2018,[125] to June 26, 2019, with a total of three tankōbon volumes.

[132] Toma, Mikoto, Accelerator, Kuroko Shirai, and Kazari Uiharu appear as playable characters in Dengeki Bunko: Crossing Void, a 2018 mobile game developed by 91Act and Sega.

[150] Leroy Douresseaux from Comic Book Bin praised the volume he reviewed, stating the art by Chuya Kogino fits the series perfectly.

[154] Like Beveridge and Wolf, Carl Kimlinger from Anime News Network also offered praise to the series for the characters and action, while criticizing for being a bit generic at times.