UFC 66: Liddell vs. Ortiz was a mixed martial arts (MMA) pay-per-view event held by the Ultimate Fighting Championship on December 30, 2006 at the MGM Grand Garden Arena in the Las Vegas suburb of Paradise, Nevada.

UFC 66's main event was a championship fight with two of the UFC's biggest light heavyweight stars, Light Heavyweight Champion Chuck Liddell defending his title against former champion Tito Ortiz.

[4] The co-main event saw Forrest Griffin take on "The Dean of Mean" Keith Jardine.

The card also saw the return of former Heavyweight Champion Andrei Arlovski and The Ultimate Fighter 3 winner Michael Bisping's first bout in the UFC since winning that season.

At the time, it was estimated to be the UFC's biggest pay-per-view success with just over 1 million buys.