Kick-Ass (also known as Hit-Girl & Kick-Ass, or simply Hit-Girl) is a media franchise based on the adventures of the superhero of the same name and its spinoff, created by Mark Millar and John Romita Jr. Set in the Millarworld, it began in 2008 with Marvel's Kick-Ass, followed by the anthology Millarworld Annual from 2016 to 2017, two stand-alone sequel series, Kick-Ass – The New Girl and Hit-Girl, from 2018 to 2020, and two crossover series, Kick-Ass vs. Hit-Girl and Big Game, in 2020 and 2023. In the series, Hit-Girl is a young vigilante (later a Kingsman agent) going around the world stopping crime in violent ways, while Kick-Ass has had three people take the mantle, a hero (Dave Lizewski), a sidekick (Paul McQue), and a villain (Patience Lee).

Kick-Ass, co-written and directed by Matthew Vaughn and also co-written by Jane Goldman, was released in March 2010. The film stars Aaron Taylor-Johnson and Chloë Grace Moretz. A sequel to this film, Kick-Ass 2, written and directed by Jeff Wadlow, was released in August 2013. Adaptations of the films have been published, and numerous Kick-Ass video games have been released since 2010. In January 2024, Matthew Vaughn revealed that a new trilogy of Kick-Ass films are in the works, and that the first two films, directed by Damien Walters and titled Stuntnuts: The Movie and Stuntnuts Does School Fight, had secretly been greenlit, cast, and had completed filming.

Created by Mark Millar and John Romita Jr., the Hit-Girl & Kick-Ass franchise is set in Millar's shared universe, the Millarworld, first established at the conclusion of Book Four of The Dave Lizewski Years, which makes reference to the events of Wanted, Nemesis, Kingsman, Superior, and MPH, with Jupiter's Legacy and Supercrooks existing as fiction within the franchise, leading into the crossover miniseries Big Game, released in 2023 following extensive development hell.

The Kick-Ass franchise began in 2008 with Book One of The Dave Lizewski Years, originally published as Kick-Ass. Books Two, Three, and Four, originally respectively published as Hit-Girl, Kick-Ass 2 and Kick-Ass 3, followed 2010–2014. The original series was rebranded as The Dave Lizewski Years following the release of stand-alone sequel series The New Girl and Hit-Girl in 2018, and heavily edited to remove scenes of violence and swearing, and all mention of Dave Lizewski's identity as Kick-Ass being revealed to the world in the third volume, a plot point ignored in the fourth volume. The series follows Dave (initially a teenager) as he sets out to become a real-life superhero over the course of several years as Kick-Ass, who joins forces with existing vigilante Hit-Girl to take on the New York Mafia, their actions bringing an influx of supervillains and heroes into the world.

In 2016 and 2019, Mark Millar published the Millarworld Annual, an anthology annual consisting of one-shot specials containing winning entries from the online contest for up-and-coming creators held by Millar in 2015 and 2016), whose stories would be published within the canon of the Millarworld. The 2016 annual Millarworld Annual 2016 would contain the stories Kick-Ass: Blindsided (written by Ricardo Mo, and illustrated by Ifesinachi Orkiekwe) and Hit-Girl: Mindy's ABCs (written by Mark Abnett, and illustrated by Ozgur Yildirim), while the 2017 annual Millarworld New Talent Annual 2017 would contain the story Kick-Ass: Trick or Cheat (written by Emma Sayle, and illustrated by Edgy Ziane).

As of February 14, 2018, a new Kick-Ass series from Image Comics, titled Kick-Ass – The New Girl, went into publication, featuring an adult female protagonist named Patience Lee, an Afghanistan war veteran and single mother who dons the Kick-Ass costume and mantle to clear her family's financial debts by initially robbing high-profile criminals, eventually becoming a crime boss and taking over the former crime bosses' territories as the supervillain Kick-Ass.

On February 21, 2018, the first issue of a Hit-Girl series from Image Comics was published, with a successive change of writers and artists for each story arc; Frank Quitely, Eduardo Risso, Rafael Albuquerque, Kevin Smith, Daniel Way and Pete Milligan named as the authors involved for each arc, from Season One: Hit-Girl In Colombia, Canada, and Rome, and Season Two: Hollywood, Hong Kong, and India. The title sees Mindy McCready leaving America to carry on her fight for justice on a worldwide scale, depicting events mentioned in the epilogue of Book Four of The Dave Lizewski Years, serving as a sequel to the main events of the series.

Kick-Ass vs. Hit-Girl, a five-issue series depicting the first confrontation between Hit-Girl and Patience Lee, went into publication on November 11, 2020, serving as the fourth and final volumes of Kick-Ass – The New Girl and the seventh and final volume of Hit-Girl.