.hack//Quantum is an animated three episode OVA series for the .hack franchise, produced by Kinema Citrus and presented by Bandai Visual. It was initially scheduled to be released in November 2010, but it was later changed. The first episode was released on January 28, 2011 with the following two episodes to be released in one month intervals. Excluding the all-CGI animation movie .hack//G.U. Trilogy, it is the first animated OVA project not to be produced by Bee Train. It is not related to a planned CGI movie tie-in to the newest game in the .hack series, .hack//Link. Masaki Tachibana of Tokyo Magnitude 8.0 directed the OVA project and .hack// writer Tatsuya Hamazaki scripted. Kinema Citrus animated the series and Kow Otani composed the music. Yuuka Nanri performed the theme song for the series. At Anime Weekend Atlanta 2011, Funimation announced that it had licensed the series and it was released on DVD and Blu-ray on February 14, 2012, making it the first in the franchise not to be licensed by Bandai Entertainment. The UK release was published by MVM Entertainment on July 9, 2012.

Kow Otani is a Japanese composer. He is best known for creating the soundtracks for the Heisei Gamera trilogy, Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack, Mobile Suit Gundam Wing, and Shadow of the Colossus.