Guin Saga (グイン・サーガ, Guin Sāga) is a best-selling heroic fantasy novel series by the Japanese author Kaoru Kurimoto, in continuous publication since 1979. A record 100 volumes were originally planned, but the current total stands at 150 volumes and 27 side-story novels, with the last twenty volumes and six side stories being published posthumously. Kurimoto was working on the 130th volume of Guin Saga up until May 23, 2009, after which point she became too ill to write and died three days later. After the 100th book in the series was published in 2005, an event to celebrate this was held in Tokyo, with 600 attending. Guin Saga is the longest single-writer's work in the world, with total sales of 30 million copies.

The main story of Guin Saga resumed on November 8, 2013, four years after the passing of the original author. Yū Godai published Volume 131 Parro no Ankoku on that date, followed by Yume Yohino's Volume 132 Cylon no Banka in December 2013.

The story centers around a mysterious warrior named Guin, an amnesiac with a leopard mask magically affixed to his head. Remembering nothing but his fighting instincts and the word "Aurra", he confronts a world laden with danger, intrigue, and magic.

Painted covers and interior illustrations for volumes 1-19 (1979–1984) were done by Naoyuki Kato. Noted artist Yoshitaka Amano then took the reins until vol. 57 (1997), upon which time he was replaced by Jun Suemi. Shinobu Tanno, whose style closely resembles Suemi's, has been the series artist since vol. 88 (2003) until the final 130th book in 2009.

American publisher Vertical has released the first five volumes, translated into English by known game translator Alexander O. Smith. The English editions have drawn praise comparing the series to The Lord of the Rings and Conan the Barbarian. The novels have also been translated into German, French, Russian, Italian, Korean and Chinese. The first three novels were released in hardback and paperback editions, the rest only in paperback.

There are two manga based on the Guin Saga. The Guin Saga Manga: The Seven Magi (グイン・サーガ七人の魔道師) is based on a gaiden (side-story) from the Guin Saga novels, where Guin is now King of Cheironia and must protect his kingdom from a magical plague. The story was originally published as a novel in 1981 and was adapted to manga, which first volume was released in February 2001. It is illustrated by Kazuaki Yanagisawa, was published in Japan by Media Factory, and has been released in English in three volumes by Vertical.

The other manga is based on the early part of the story and is adapted to manga format by Hajime Sawada, as part of the Jive series Kurimoto Kaoru The Comic (栗本薫 The Comic), adapting Kurimoto's works to manga form.

On April 12, 2005, Micott & Basara (Japanese investors) announced plans to create an anime based on Guin Saga. In October 2008 more details surfaced which revealed Atsushi Wakabayashi is directing the anime, while famous video game composer Nobuo Uematsu is creating the score. This is Uematsu's first full soundtrack for an anime, and Wakabayashi's first directing role. Animation production was handled by Satelight and the background art by Studio Easter. The anime debuted on April 5, 2009. On April 3, 2009, an English-dubbed trailer was posted on the anime's official website. On May 7, 2010, North American anime licensor Sentai Filmworks announced that they have acquired the series. Sentai, along with distributor Section23 Films, released part one of the series on DVD on March 29, 2011. Section23 had previously announced a Blu-ray release, but it has been postponed indefinitely. On May 8, 2012, Sentai Filmworks released a complete Guin Saga BD Set encompassing the entire series.