Giant-Size X-Men #1 is a special issue of the X-Men comic book series, published by Marvel Comics in 1975. It was written by Len Wein and illustrated by Dave Cockrum. Chris Claremont has an uncredited plot assist. (He came up with the idea of Polaris using her powers to propel Krakoa into space.) Though not a regular issue, it contained the first new X-Men story in five years, titled "Second Genesis." The issue serves as a link between the original X-Men and a new team. Chronologically it is placed after X-Men #66 and before X-Men #94. The 68-page book was published with a May 1975 cover date and distributed to newsstands in February of that year. The issue has been cited as a start point of the bronze age of comics, and is notable for expanding the membership of The X-Men from beyond the white American cast to one of a more international flavour, an attempt to attract more readers from outside the US,^[1] even if some characters were portrayed somewhat stereotypically.^{[2][3][4][5][6]}

The X-Men title stopped producing new stories after #66 in March 1970. From December 1970 through April 1975, Marvel reprinted many of the older X-Men issues as #67–93. Following the May publication of Giant-Size X-Men #1, Marvel began again publishing new issues of X-Men with #94 in August 1975.^[7]

The comic also collects reprints from X-Men #43, #47 and #57.^[8]

The story opens in medias res, with Professor X recruiting a new team of X-Men, to rescue the original X-Men (Marvel Girl, Iceman and Angel [but not Beast, who had left the team], plus X-Men recruits Havok and Polaris), who had disappeared on a mission to the island of Krakoa, with only their leader Cyclops escaping. The new team consists of Sunfire and Banshee, who had been introduced in earlier X-Men comics; Wolverine, who had made his first appearance in The Incredible Hulk #181 (Oct. 1974); and the newly created Storm, Nightcrawler, Colossus, and Thunderbird. These members are gathered from all over the world, and Professor X uses his telepathic powers to teach them all English so that they can communicate with each other.

The team soon learns that Krakoa is not just an island, but a giant mutant as well. Despite personality clashes among the individual members, as well as a fatality, the new team succeeds in rescuing the old X-Men and destroying the entity by shooting it into outer space with Polaris' power. The issue ends by posing the question of the future of a 13-member X-Men team.

The later storyline "Deadly Genesis" offers a ret-con of this story, which tells how Professor X had initially recruited a different team before the events in this issue.

• Story, edits — Len Wein
• Pencils, cover inks — Dave Cockrum
• Cover pencils — Gil Kane
• Inks — Dave Cockrum & Peter Iro
• Letters — John Costanza
• Colors — Glynis Wein

The "Second Genesis" story was reprinted in Classic X-Men #1 in September 1986, with substantial editing to reduce its length, and a new backup story by Claremont and John Bolton bridging the gap between this and the following issue, Uncanny X-Men #94.

Marvel published a second issue of Giant-Size X-Men later in 1975. This November issue had no new material, instead featuring reprints of stories from X-Men #57, #58, and #59, written by Roy Thomas and illustrated by Neal Adams.^[9]