Monster (stylized in all caps) is a Japanese manga series written and illustrated by Naoki Urasawa. It was published by Shogakukan in their seinen manga magazine Big Comic Original between December 1994 and December 2001, with its chapters collected in 18 tankōbon volumes. The story revolves around Kenzo Tenma, a Japanese surgeon living in Düsseldorf, Germany whose life enters turmoil after getting himself involved with Johan Liebert, one of his former patients, who is revealed to be a dangerous serial killer.

Urasawa later wrote and illustrated the novel Another Monster, a story detailing the events of the manga from an investigative reporter’s point of view, which was published in 2002. The manga was adapted by Madhouse into a 74-episode anime television series, which aired on Nippon TV from April 2004 to September 2005. The manga and anime were both licensed by Viz Media for English releases in North America, and the anime was broadcast on several television channels. In 2013, Siren Visual licensed the anime for Australia.

Monster was Urasawa’s first work to receive international acclaim and success; the manga has sold over 20 million copies, making it one of the best-selling manga series of all time. The manga has won several awards, including the 46th Shogakukan Manga Award and the Japan Media Arts Festival. Its anime adaptation has been called one of the best anime series of its decade.