WrestleMania XX was the 20th annual WrestleMania professional wrestling pay-per-view (PPV) event produced by World Wrestling Entertainment (WWE). It featured professional wrestlers from both of the promotion's two brand divisions – Raw and SmackDown!. The event took place on March 14, 2004, at Madison Square Garden in New York City. It was the third WrestleMania at Madison Square Garden (after WrestleMania I in 1985 and WrestleMania X in 1994) and the fourth of six WrestleManias in the New York metropolitan area (alongside WrestleMania I, 2, X, 29, and 35). To this date it is the last WrestleMania to have been held at the Garden. Its calendar date of March 14 also stands as the earliest that WrestleMania has ever been held in any year.

The match card featured two main events. The pay-per-view main event, which was also the main match for the Raw brand, was a triple threat match for the World Heavyweight Championship, which saw champion Triple H defending the world title against Shawn Michaels, and that year's Royal Rumble match winner, Chris Benoit. Benoit won the match, making Triple H submit via the Crippler Crossface, resulting in his first and only world championship in the WWE. The main match for the SmackDown! brand featured Eddie Guerrero versus Kurt Angle for the WWE Championship, which Guerrero won by a Small Package pin. The event also featured the return of The Undertaker in his Deadman persona, who defeated Kane, after a Tombstone Piledriver. John Cena made his in-ring WrestleMania debut at the event, by defeating Big Show to win his first title in WWE, the WWE United States Championship.

Also on the card was a match between Goldberg and Brock Lesnar, with Stone Cold Steve Austin as the special guest referee. This was both Lesnar's and Goldberg's final match with WWE until the 2012 edition of Extreme Rules, and the 2016 edition of Survivor Series, respectively. After Goldberg won the match following a Jackhammer, both men were given a Stone Cold Stunner by Austin on their way out. The event also featured the in-ring return of The Rock, teaming up with Mick Foley and reuniting the Rock 'n' Sock Connection to take on Evolution in a 3-on-2 Handicap match, in which Evolution were victorious. This would be The Rock's final match in WWE until Survivor Series 2011.

The event grossed $2.4 million in ticket sales, making the pay-per-view the highest grossing event ever for WWE at Madison Square Garden. More than 20,000 people from 16 countries and 48 states attended the event, which was also televised in more than 90 countries. The event generated an estimated $13.5 million of economic activity for New York City and created an equivalent of 96 full-year jobs.