Log Horizon first starts out as a novel series by Mamre Touno. It spawned multiple manga adaptations and an anime series.
Written by Mamare Touno and illustrated by Kazuhiro Hara.
Illustrated by Motoya Matsu and published by ASCII Media Works. Ran in the Dengeki Daioh magazine on January 27, 2012.
Illustrated by Kazuhiro Hara and published by Enterbrain. Ran in the Famitsu Comic Clear magazine on May 18, 2012.
Illustrated by Koyuki and published by Fujimi Shobo. Ran in the Age Premium magazine on July 9, 2012.
Illustrated by Sōchū and published by Enterbrain. Ran in the Comic B's LOG on December 21, 2012.
Directed by Shinji Ishihara and written by Toshizo Nemoto. Produced by Satelight and broadcast on the NHK E channel.