The 2021 SummerSlam was the 34th annual SummerSlam professional wrestling pay-per-view (PPV) and livestreaming event produced by WWE. It was held for wrestlers from the promotion's Raw and SmackDown brand divisions. The event took place on Saturday, August 21, 2021, at Allegiant Stadium in the Las Vegas suburb of Paradise, Nevada, and was the first SummerSlam to livestream on Peacock. It was not the first SummerSlam to take place on a Saturday, but it was the first to air live on a Saturday, as well as the first SummerSlam to take place in a stadium since the 1992 event. It was also WWE's first event to air in theaters in the United States in addition to the other broadcast outlets.

Due to April's WrestleMania 37 having to be held at a reduced capacity because of the COVID-19 pandemic, SummerSlam was promoted as WWE's "biggest event of 2021". The event had an attendance of 51,326, marking the third-largest crowd in the event's history and the second highest-grossing SummerSlam event of all time. This would also be the final SummerSlam to have creative involvement of Vince McMahon, who created SummerSlam in 1988, however, Vince returned to the company in January 2023 after leaving in mid-2022.

Eleven matches were contested at the event, including one on the Kickoff pre-show. In the main event, Roman Reigns defeated John Cena to retain SmackDown's Universal Championship. In other prominent matches, Bobby Lashley defeated Goldberg to retain Raw's WWE Championship, Edge defeated Seth Rollins, Charlotte Flair defeated defending champion Nikki A.S.H. and Rhea Ripley in a triple threat match to win her record sixth Raw Women's Championship, Damian Priest defeated Sheamus to win Raw's United States Championship, and in the opening bout, RK-Bro (Randy Orton and Riddle) defeated AJ Styles and Omos to win the Raw Tag Team Championship.