WrestleMania 21 was the 21st annual WrestleMania professional wrestling pay-per-view (PPV) event produced by World Wrestling Entertainment (WWE). It was held for wrestlers from the promotion's Raw and SmackDown! brand divisions. The event took place on April 3, 2005, at Staples Center in Los Angeles, California.

WrestleMania is a professional wrestling event held annually between mid-March and mid-April by the American company WWE, the world's largest professional wrestling promotion. Since premiering in 1985, 40 events have been held, with its most recent 40th edition occurring at Lincoln Financial Field in Philadelphia, Pennsylvania on April 6 and 7, 2024. WrestleMania was WWE's first-ever pay-per-view (PPV) produced and is the most successful and longest-running professional wrestling event in history. The event has been broadcast through traditional PPV since 1985 and has been available via livestreaming since WrestleMania XXX in 2014, which was WWE's first major event available through this medium. WrestleMania was conceptualized by former WWE executive chairman Vince McMahon and named by ring announcer and WWE Hall of Famer Howard Finkel. It is the company's flagship event and along with Royal Rumble, SummerSlam, Survivor Series, and Money in the Bank, it is referred to as one of the "Big Five", WWE's five biggest annual events of the year.