Zatch Bell!, known in Japan as Konjiki no Gash!! (Japanese: 金色のガッシュ!!, Hepburn: Konjiki no Gasshu!!, "Golden Gash!!"), is a Japanese manga series written and illustrated by Makoto Raiku. It was serialized in Shogakukan's shōnen manga magazine Weekly Shōnen Sunday between January 2001 and December 2007, with its chapters collected in thirty-three tankōbon volumes. The series follows the title character Zatch Bell, a mystical being called a Mamodo, who is partnered with a 14-year-old schoolboy Kiyo Takamine for a once-a-millennium tournament on Earth that determines the right to rule the Mamodo world as king. During their adventure, Zatch and Kiyo encounter and battle various Mamodo and their human partners, and meet allies who aid Zatch in his quest to become a kind king.

Zatch Bell! was later adapted into an anime television series produced by Toei Animation. The series aired for 150 episodes on Fuji TV from April 2003 to March 2006. In addition to an array of licensed merchandise, the franchise also spawned a series of video games and two animated theatrical films. Viz Media licensed both the manga and anime series for English-language localization in North America in 2005; only twenty-five volumes of the manga were published until 2009. The anime series ran in the United States on Cartoon Network's Toonami and Miguzi programming blocks from 2005 to 2007 for seventy-seven episodes, and in Canada on YTV's Bionix programming block from 2005 to 2008; in all, 104 episodes were dubbed in English.

By March 2017, the Zatch Bell! manga had over 23.8 million copies in circulation, including digital versions, making it one of the best-selling manga series. In 2003, the series won the 48th Shogakukan Manga Award for the shōnen category. The manga has received generally positive reviews from critics. It was praised for its unique characters, humor, and overall concept. The television adaptation has a more mixed reception, with criticism largely focused on the visuals, graphical violence, and voice acting, particularly for the English dub.

A sequel to the original manga, titled Konjiki no Gash!! 2, began digital distribution in March 2022.