GENSHIKEN (げんしけん) is a very popular manga created by Kio Shimoku about living in an otaku club. Is basically a "slice-of-life" comedy series focusing in otaku life and its consequences.
The title is a shortening of the club's official name, GENdai SHIkaku Bunka KENkyūkai (現代視覚文化研究会), which is translated as The Society for the Study of Modern Visual Culture.
Serialized in Kodansha's Afternoon from 2002-2006, the manga series continued for a second season as Genshiken II (Genshiken Nidaime or Genshiken Second Generation), which was released in December 2010 and ended in August 2016.
The original manga was also adapted into two separate TV anime series by Genco in 2004 and 2007, as well as a 3 episode OVA in 2006. Additionally, Kio Shimoku announced in the manga that a new TV anime adaptation of the Second Generation manga was in the works with the title Genshiken Nidaime (げんしけん 二代目 - Genshiken Second Generation), later airing in Japan from July 6 to September 29, 2013.
A Genshiken Second Season OAD or Original Animation DVD was bundled with the limited edition of the 15th volume of the Genshiken manga. It was released in Dec 20, 2013 with the title Genshiken Nidaime No Roku DVD (げんしけん オリジナルアニメDVD). The story is set between the events of Genshiken 2 and the Genshiken Nidaime series so none of the new characters from Nidaime appear in this anime.
A spin-off, Kujibiki Unbalance, was produced by Ajia-do Animation Works in 2006, along with a manga, illustrated by Koume Keito.
Spotted Flower, a manga periodically illustrated and produced by Kio outside of Afternoon since 2009, is loosely based on Genshiken.