WWF Invasion (also typeset as InVasion) was a professional wrestling pay-per-view (PPV) event produced by the World Wrestling Federation (WWF, now WWE). It took place on July 22, 2001, at the Gund Arena in Cleveland, Ohio. This event was initially planned to be the fourth Fully Loaded PPV, as it was advertised at the King of the Ring event, which immediately preceded Invasion, although the decision to replace Fully Loaded was made in May. Invasion was the first pay-per-view to feature the ongoing Invasion storyline, which featured wrestlers from the WWF taking on The Coalition, a combined force of wrestlers from World Championship Wrestling (WCW) and Extreme Championship Wrestling (ECW), later known as The Alliance. The event featured WWF wrestlers facing WCW and ECW wrestlers.

The main event, dubbed the "Inaugural Brawl," was a five-on-five tag team match between Team WWF and Team WCW/ECW. The other main match was a singles match for the WWF Hardcore Championship between Rob Van Dam and Jeff Hardy. With a buyrate of 775,000, the event is the highest grossing non-WrestleMania pay-per-view in WWE history.

Following the conclusion of the storyline, the event's July slot was given to Vengeance in 2002 when Armageddon returned that year; Vengeance temporarily replaced Armageddon in December 2001 due to the September 11 attacks.