OnePunch-Man is a Japanese superhero manga series originally released as a webcomic in early 2009. It tells the story of Saitama, an independent superhero who, having trained to the point that he can defeat any opponent with a single punch, grows bored from a lack of challenge. He sets out to find powerful opponents, while making allies of other heroes as well.

A digital manga remake, illustrated by Yusuke Murata, began publication on Shueisha's Tonari no Young Jump website in June 2012. Its chapters are periodically compiled and published into individual tankōbon volumes. As of August 2025, 34 volumes have been released. In North America, Viz Media licensed the remake manga for English language release and has serialized it in its Weekly Shonen Jump digital magazine.

An anime adaptation produced by Madhouse was broadcast in Japan from October to December 2015. A second season, produced by J.C.Staff, was broadcast from April to July 2019. A third season, also by J.C.Staff, is set to premiere in October 2025. Licensed in North America by Viz Media, the series aired its first season in the United States on Adult Swim's Toonami programming block from July to October 2016. The second season aired on the block from October 2019 to January 2020.

By June 2012, the original webcomic manga surpassed 7.9 million hits. By August 2025, the manga remake had over 34 million copies in circulation, making it one of the best-selling manga series of all time.