X2 (also known as X2: X-Men United, X-Men 2: X-Men United, and X-Men 2) is a 2003 superhero film based on the fictional characters the X-Men. Directed by Bryan Singer, it is the second part of the X-Men film series, following X-Men (2000) and preceding X-Men: The Last Stand (2006). It stars an ensemble cast including Hugh Jackman, Patrick Stewart, Ian McKellen, Alan Cumming, Famke Janssen, Anna Paquin, Shawn Ashmore, Aaron Stanford, Rebecca Romijn, James Marsden, Halle Berry and Kelly Hu. The plot, inspired by the graphic novel God Loves, Man Kills, pits the X-Men and their enemies, the Brotherhood, against the genocidal Colonel William Stryker (Brian Cox). He leads an assault on Professor Xavier's school to build his own version of Xavier's mutant-tracking computer Cerebro, in order to destroy every mutant on Earth.

Development phase for X2 began shortly after X-Men. David Hayter and Zak Penn wrote separate scripts, combining what they felt to be the best elements of both scripts into one screenplay. Michael Dougherty and Dan Harris were eventually hired for rewrite work, changing characterizations of Beast, Angel and Lady Deathstrike. Sentinels and the Danger Room were set to appear before being deleted because of budget concerns. Filming began in June 2002 and ended that November. Most of the filming took place at Vancouver Film Studios, the largest soundstage in North America. Production designer Guy Hendrix Dyas adapted similar designs of John Myhre from the previous film. X2 was released in the United States on May 2, 2003 and became both a critical and financial success, earning eight nominations at the Saturn Awards and grossing approximately US$408 million worldwide.