X-Men: The Last Stand (also marketed as X3: The Last Stand, or X-Men 3) is a 2006 superhero film based on the X-Men comic books published by Marvel Entertainment Group. It is the sequel to X2 (2003) and the third installment in the X-Men film series, as well as the final film of the original X-Men trilogy. It was directed by Brett Ratner and features an ensemble cast including Hugh Jackman, Halle Berry, Ian McKellen, Famke Janssen, Anna Paquin, Kelsey Grammer, James Marsden, Rebecca Romijn, Shawn Ashmore, Aaron Stanford, Vinnie Jones, and Patrick Stewart. Written by Simon Kinberg and Zak Penn, the film is loosely based on two X-Men comic book story arcs, "Gifted" and "The Dark Phoenix Saga", with a plot that revolves around a "mutant cure" that causes serious repercussions among mutants and humans, and on the resurrection of Jean Grey who unleashes a dark force.

Bryan Singer, who had directed the two previous films, X-Men and X2, decided to leave the sequel to work on Superman Returns (2006). X2 composer and editor John Ottman and X2 writers Dan Harris and Michael Dougherty also left to work on Superman Returns, as did James Marsden, who had very limited screen time in The Last Stand before his character was killed off due to his departure from the film. Singer had not even defined the storyline for a third film. Matthew Vaughn, who co-wrote the script (though uncredited) and was initially hired as the new director, left due to personal and professional issues, and was replaced with Ratner. Filming took place from August 2005 to January 2006 with a budget of $210 million, and was consequently the most expensive film made at the time of its release. It had extensive visual effects created by 11 different companies.

X-Men: The Last Stand premiered in the Out of Competition section at the 2006 Cannes Film Festival, and was released theatrically in the United States on May 26 by 20th Century Fox. It grossed approximately $459 million worldwide, becoming the seventh-highest-grossing film of 2006; it was at the time the highest-grossing film in the series and after 2018 stood as the fourth-highest-grossing film of the franchise. It received mixed reviews from critics and was deemed inferior to its predecessors.

A standalone sequel, The Wolverine, was released in 2013; it was followed by X-Men: Days of Future Past in 2014, which retconned the events of The Last Stand. Several actors reprise their roles in Marvel Cinematic Universe films, including Stewart in Doctor Strange in the Multiverse of Madness (2022), Grammer in The Marvels (2023), Jackman and Stanford in Deadpool & Wolverine (2024), and McKellen, Grammer, Marsden, Romijn, and Stewart in Avengers: Doomsday (2026).