"Days of Future Past" is a storyline in the Marvel Comics comic book The Uncanny X-Men issues #141–142, published in 1981. It deals with a dystopian future in which mutants are incarcerated in internment camps. An adult Kate Pryde transfers her mind into her younger self, the present-day Kitty Pryde, who brings the X-Men to prevent a fatal moment in history that triggers anti-mutant hysteria.

The storyline was produced during the franchise's rise to popularity under the writer/artist team of Chris Claremont, John Byrne and Terry Austin. The dark future seen in the story has been revisited numerous times, and was the basis for the 2014 similarly-titled feature film X-Men: Days of Future Past, wherein Wolverine is sent back in time. In 2001, fans voted the first issue of this storyline the 25th greatest Marvel comic.

The Official Handbook to the Marvel Universe: Alternate Universes 2005 gave the numerical designation for the original "Days of Future Past" timeline as Earth-811 in the Marvel Multiverse.

The storyline alternates between the present year of 1980 and the future year of 2013. In the future, Sentinels rule a dystopian United States, and mutants are hunted and placed in internment camps. Having conquered North America and hunted all mutants and other superhumans, the Sentinels are turning their attention to the rest of the world. On the eve of a feared nuclear holocaust, the few remaining X-Men send Kitty Pryde's mind backward through time, to possess the body of her younger self and to prevent a pivotal event in mutant–human history and the cause of these events: the assassination of Senator Robert Kelly by Mystique's newly reassembled Brotherhood of Evil Mutants.

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