K-On! began as a four-panel comic-strip manga written and illustrated by Kakifly. The manga started serialization in Houbunsha's Manga Time Kirara manga magazine in the May 2007 issue, and ended in the October 2010 issue.

The manga was licensed by Yen Press for an English release in North America. There is an anthology entitled Minna de Untan!, which features several guest strips from various artists. An official anthology, K-On! Anthology Comic? (けいおん!アンソロジーコミック, Keion! Ansorojī Komikku?), was released on November 27, 2009 by Houbunsha, and a second volume was released on April 27, 2010. An illustration book with official art and fan art from well known dōjin artists was released on January 27, 2010. 

A thirteen-episode anime adaptation directed by Naoko Yamada, written by Reiko Yoshida, and produced by Kyoto Animation aired between April 3 and June 26, 2009 on TBS in Japan. An additional OVA (original video animation) episode was released with the final DVD and BD volumes on January 20, 2010.

The single for the first season's opening theme, "Cagayake! Girls", debuted at fourth in the ranking on the Oricon weekly singles chart, selling approximately 62,000 copies. The ending theme "Don't Say 'Lazy'" debuted at second in the ranking, selling 67,000 copies. It was also awarded Best Theme Song at the 14th Animation Kobe Awards. Additionally, "Cagayake! Girls" and "Don't Say 'Lazy'" were certified Gold and Platinum by the Recording Industry Association of Japan for 100,000 and 250,000 full-track ringtone digital music downloads (Chaku Uta Full), respectively.

Season two picks up without missing a beat. All the rich backgrounds and detail are still there. The feel-good vibe is still strong and Yui is still a complete ditz. The first episode sets the tone for an even better season, and each successive episode increases in quality exponentially. Character development is top-notch, as well as giving the second-tier characters room to shine as well

The second season utilizes 2 OP's and ED's. For episodes 1-13 theOP is "GO,GO, MANIAC!", featuring Toyosaki Aki (Yui) and the ED,"Listen!" has Hikasa Yõko (Mio) taking the lead vocals. For Episodes 14-27 Utauyo!! Miracle" once again featuring Toyosaki Aki (Yui) and "No, Thank You!", by Toyosaki, Hikasa, Satō, Kotobuki, and Taketatsu, with Hikasa taking lead vocals.