The Marvel Comics anthology series What If? tells alternate reality stories outside the mainstream Marvel Universe continuity, which the company sets on what it calls Earth-616. A number of these stories have been set on alternate Earths in the Marvel Comics Multiverse (i.e., multiple universes) for which Marvel has given official numerical designations.

Volume 1 (1977–1984)

Select stories (noted above) were collected in a trade paperback, The Best of What If, in 1991. The entire series was collected in a series of seven volumes titled What If Classic from 2004 to 2010, with the exception of issues #13 and 16 and the lead story of #43 because they featured licensed characters, namely Conan the Barbarian and Fu Manchu.

Special (1988)

Volume 2 (1989–1998)

Issue #-1, What if...starring Bishop (based on Uncanny X-Men #282), was published as a part of the "Flashback" event, in which most of Marvel's series published issues numbered "-1" that were set in the past. This particular issue features an alternate backstory for Bishop, where he and Fitzroy travel back in time to before the X-Men were formed.

Marvel Alterniverse

The Alterniverse was what Marvel briefly labeled their What If stories from 1995 to 1996. The stories told under the Alterniverse label are typically one-shots and limited series, such as Ruins, Punisher: A Man Named Frank, Punisher Kills the Marvel Universe, and The Last Avengers Story.

Volume 3 (2005)

A series of What If one-shot issues was released cover-dated February 2005. The series, including the "Wha-Huh?" humor issue, was later collected into a trade paperback entitled What If: Why Not.

Volume 4 (early 2006)

The February 2006 one-shot issues took place in a single fictional universe, dubbed Earth-717 in previews, with four of the six stories more like DC's Elseworlds with various heroes in historical periods. The series was later collected into a trade paperback entitled What If: Mirror Mirror.

Volume 5 (late 2006)

The November 2006 one-shot issues were based on major storylines or crossovers: The series was later collected into a trade paperback entitled What If: Event Horizon featuring the cover from the Spider-Man one-shot.

Volume 6 (2007)

The sixth series of What If? continued the theme of the previous series of examining possible alternatives for major storylines. The series was also due to feature What If?: The New Fantastic Four, which featured the "original" New Fantastic Four with Spider-Man, Wolverine, the Ghost Rider, and the Hulk teaming up, as seen in Fantastic Four #347-349 and #374. This story was halted due to the passing of artist Mike Wieringo, and was released as a 48-Page Special as a tribute in June 2008. All the issues of this run, aside from the New Fantastic Four one, were later collected into a trade paperback simply entitled ''What If? Civil War''. The version of the "New" Fantastic Four is also erroneous, as the Ghost Rider of that time period had been Danny Ketch, not Johnny Blaze, who appears in the issue instead for unexplained reasons (in reality, Wieringo had drawn the wrong Ghost Rider in his initial pages by mistake and it was not noticed until after his death).

Volume 7 (2008)

This series continues the theme of alternatives for three recent Marvel events along with two around a classic event. The New Fantastic Four story was a sequel to the one-shot What If? released previously, seeing Iron Man replace Ghost Rider in an alternate take on the Infinity Gauntlet storyline. However, this series also features a storyline featuring the Runaways that runs through all five comics. This series was released between December 2008 and January 2009. The seventh series was later collected into a trade paperback entitled What If?: Secret Wars featuring the cover from the Secret Wars one-shot.

Volume 8 (2009)

At Fan Expo Canada '09, it was revealed a new five-part What If series would be released, featuring five one-shot issues, each with two alternatives for the focused event, except for Daredevil vs. Elektra, which had only one story. As a back-up feature in the other four one-shot issues, there is a humorous Say What? short story. The eighth series was later collected into a trade paperback entitled What If?: Secret Invasion featuring the cover from the Secret Invasion one-shot.

Volume 9 (2010)

In early September 2010, Marvel announced a series of new What If? issues, including the celebration of the 200th issue of What If?. It features a story regarding the Siege event, and a story by Stan Lee about the Watcher and Galactus. Further What If stories were released for Dark Reign, Spider-Man: Grim Hunt, a story focusing on Wolverine and his son Daken, and another on the pre-hero and villain lives of Iron Man and Doctor Doom. Those four issues also have a back-up story on Deadpool being controlled by the Venom symbiote. The Venom/Deadpool backup chapters were subsequently released as a stand-alone one-shot.

What If?: Avengers vs. X-Men (2013)

In July 2013, Marvel released a four-issue miniseries for What If based on the 2012 event Avengers vs X-Men, telling the story of what might have happened if Magneto had been more influential in Hope's development for Phoenix.

What If: Age of Ultron (2014)

In April 2014, Marvel released a five-issue miniseries for the 2013 event Age of Ultron, focusing on Wolverine and the Invisible Woman's trip back in time to kill Hank Pym in order to stop him from creating Ultron and showing the effects for the Marvel Universe if one of the other four founding Avengers had died, or if Hank had simply chosen not to create Ultron at all.

What If? Infinity (2015)

In October 2015, Marvel released a five-issue miniseries for the 2013 event Infinity that depicted alternate outcomes for Thanos' invasion of Earth and the war with the Builders. The five scenarios are the following:

What If? With Great Power (2018)

Marvel released a new series of What If? one-shot issues in October 2018, which revived the concept of the publisher's classic series that examines alternate outcomes for major storylines and alternate versions of well-known characters such as Spider-Man, Magik, the Ghost Rider, Thor, the X-Men and the Punisher. The 13th series was later collected into a trade paperback entitled ''What If? With Great Power'' featuring the cover from the Punisher one-shot.