Nisio Isin (often stylized NisiOisiN to highlight that his pen name reads the same forwards and backwards) is a Japanese novelist and manga writer. He left Ritsumeikan University without finishing his degree, but didn't need it—in 2002, at just twenty years old, he debuted with Kubikiri Cycle and immediately won the 23rd Mephisto Award.

He's best known for the Monogatari series, particularly Bakemonogatari and Katanagatari, both of which have been adapted into anime. He also wrote Death Note Another Note: The Los Angeles BB Murder Cases, which came out in English through Viz Media in 2008.

These days he works closely with Kodansha across multiple publications—Pandora, the Kodansha Box magazine, and Faust, a literary magazine that spotlights younger authors working in the light novel and otaku space. At one point, he was part of something pretty unusual: he and fellow author Ryusui Seiryoin both released twelve-volume monthly novel series simultaneously through Kodansha Box, apparently the first time two authors have ever done that from the same publisher. Del Rey Manga has also released volumes from his Zaregoto series in English.