The Danger Room facility was going to appear in the previous X-Films, but was written out due to budgetary concerns. It finally appears in this film.
Many of the actors performed their own stunts in the film.
In a June 2009 interview, Bryan Singer admitted that he regretted declining to direct this film in favor of Superman Returns (2006), confessing that he realized his mistake "before I was watching [the third X-Men film], during watching it, after watching it."