UFC 40: Vendetta was a mixed martial arts event held by the Ultimate Fighting Championship on November 22, 2002, at the MGM Grand Garden Arena on the Las Vegas Strip in Paradise, Nevada.

The event was broadcast live on pay per view in the United States, and later released on DVD.

UFC 40 also contained a Welterweight Title Bout between Matt Hughes and Gil Castillo.

This was important for the sport of mixed martial arts because had UFC 40 been a failure, the possibility existed that Zuffa would have eventually sold the UFC and cut their losses; Zuffa was largely responsible for bringing mixed martial arts to the North American mainstream audience in the coming years, and without them, there was a good possibility the sport of mixed martial arts would have remained underground outside Japan.

Ken Shamrock and Tito Ortiz both appeared on The Best Damn Sports Show Period and engaged in trash talk on live television.

In fact, Danny Sheridan, the USA Today oddsmaker, was present during the card.