Yu-Gi-Oh! (Japanese: 遊☆戯☆王, Hepburn: Yū Gi Ō; lit. 'Game King') is a Japanese manga series written and illustrated by Kazuki Takahashi. It was serialized in Shueisha's shōnen manga magazine Weekly Shōnen Jump from September 1996 to March 2004, with its chapters collected in 38 tankōbon volumes. The series follows Yugi Mutou, a teenager who solves the ancient Egyptian Millennium Puzzle. This revives an ancient gambling spirit sealed inside the Puzzle, who commonly possesses Yugi to solve conflicts with various games. Yugi gradually learns of the spirit, with whom he eventually forms a friendship as he and his friends aim to discover the spirit's origin. By its later arcs, the manga largely shifts its focus to the collectible card game Duel Monsters (originally known as Magic & Wizards), where opposing players "duel" each other in mock battles of fantasy monsters.

The manga spawned a media franchise, which includes multiple anime series, spin-off manga, video games, and a real-world card game adapted from the fictional Duel Monsters game. The original series was adapted into two anime series: an eponymous series produced by Toei Animation, which aired from April to October 1998; and Yu-Gi-Oh! Duel Monsters, produced by NAS and animated by Gallop, which aired from April 2000 to September 2004. The franchise also includes four films, with an eponymous short film based on the Toei series released March 1999, and the Duel Monsters anime leading to the feature films Pyramid of Light (2004) and Bonds Beyond Time (2010), the latter also crossing over with the spin-off series Yu-Gi-Oh! GX and Yu-Gi-Oh! 5D's. Yu-Gi-Oh! The Dark Side of Dimensions, released in 2016, is set after the original manga series.

By July 2022, the manga had over 40 million copies in circulation, making it one of the best-selling manga series of all time. The franchise generated $5 billion in retail sales, making it one of the highest-grossing media franchises of all time.

Yu-Gi-Oh! follows Yugi Mutou, a timid high schooler who is frequently bullied. Yugi loves to play games and, at the beginning of the series, is solving the Millennium Puzzle (千年パズル, Sennen Pazuru), an Ancient Egyptian artifact, hoping that it will grant him his wish of making friends. Yugi eventually completes the Puzzle, causing his body to become the host to a mysterious spirit with the personality of a gambler. From that moment onwards, whenever Yugi or any of his friends is threatened, the spirit, briefly possessing Yugi, challenges the antagonist to Shadow Games (闇のゲーム, Yami no Gēmu; lit. 'Game of Darkness') that reveal that person's true nature, with the loser often being subjected to an adverse Penalty Game (罰ゲーム, Batsu Gēmu). Yugi and his friends gradually learn of the spirit's existence, referring to him as the "other Yugi".

As the series progresses, Yugi and his friends learn that the spirit is actually that of a nameless Pharaoh of Ancient Egypt, who had lost his memories after being sealed inside the Puzzle. As Yugi and his companions attempt to help the Pharaoh regain his memories, they find themselves going through many trials as they wager their lives facing off against those who wield the other Millennium Items (千年アイテム, Sennen Aitemu) and the dark power of the Shadow Games.