A Certain Scientific Railgun (Japanese: とある科学の超電磁砲レールガン, Hepburn: Toaru Kagaku no Rērugan) is a Japanese manga series written by Kazuma Kamachi and illustrated by Motoi Fuyukawa, which began serialization in the April 2007 issue of ASCII Media Works' Dengeki Daioh magazine. The manga is a spin-off of Kamachi's A Certain Magical Index light novel series, taking place before and during the events of the main story. Seven Seas Entertainment began publishing the series in North America in June 2011. The series focuses on Mikoto Misaka and her friends—and the dangerous situations they find themselves in—as they get caught up in the matter of the Level Upper.

An anime television series adaptation by J.C.Staff aired in Japan between October 2009 and March 2010, followed by an original video animation released in October 2010. A second season titled A Certain Scientific Railgun S aired between April and September 2013. A spin-off manga series titled A Certain Scientific Railgun: Astral Buddy began serialization in Dengeki Daioh from April 2017 to July 2020. A third season titled A Certain Scientific Railgun T aired between January and September 2020. A fourth season has been announced.

In the futuristic Academy City, which is made up of 80% students, many of whom are espers possessing unique psychic powers, Mikoto Misaka is an electromaster who is the third strongest of seven espers who have been given the rank of Level 5. The series focuses on the exploits of Mikoto and her friends Kuroko Shirai, Kazari Uiharu, and Ruiko Saten, prior to and during the events of A Certain Magical Index.