Random Trivia For This Title:
- Prints were sent out to UK cinemas under the fake name "New Hampshire" - a reference to the state's "Live Free or Die" motto and the movie's original title - in spite of the title being changed to Die Hard 4.0 in European territories.
- In the beginning of the film, John McClane and Lucy have an argument that eventually leads to them discussing her use of her mother's last name, "Gennaro." A similar argument takes place in Die Hard, when McClane is searching for the location of his wife, Holly, in the Nakatomi building. He does not find her under "McClane," but does find her under her maiden name "Gennaro."
- In addition to the 'Agent Johnson' reference, several other elements from the first film are revisited as series trademarks. Among them are: crawling on broken glass, use of air-ducts, elevator shafts, and maintenance areas in corporate buildings, a henchman falling down stairs, an inquiry on the E.T.A. of a helicopter, and McClane's "Yippie Ki Yay" catchphrase.
- When McClane throws Russo down the stairs, the stuntman landed so hard that his impact dented one of the thick metal steps.
- The name "Tovarek", which Mai Lihn uses as an FBI agent, is a Polish word and one of it meanings is "hot chick" (the correct Polish word is "towarek", but it's pronounced like this).
- A water treatment facility near Los Angeles doubled as the film's Woodlawn Social Security Administration building. The facility has miles of underground tunnels, and was also used in Die Hard 2 when Bruce Willis runs through tunnels under the airport.
- When McClane is driving toward the helicopter, he says, "You think a traffic jam, throwing a car at me is gonna stop me, huh?" Director Len Wiseman dubbed the last part of this line ("Gonna stop me"), imitating the voice of Bruce Willis.
- It took four months to assemble and complete the video montage of speeches from United States presidents. The goal was to create a video representation of a ransom note.
- Kal Penn and [?] Brad Renfro both auditioned for the role of Matt before it went to Justin Long.
- The film's climax originally involved McClane racing alongside an exploding gas pipeline on a motorcycle with Matt in a sidecar. The idea evolved into Gabriel trying to kill McClane and Matt by routing gas to their location through the pipelines.
- While the line "Yippee-ki-yay, mother*$@^#%!" is used in all Four [Die Hard] movies, a gunshot masks the '*$@^#%!' part in the latest installment. It also translates in Urdu to "here eat this"
- Director Len Wiseman credits actor Timothy Olyphant (Thomas Gabriel) with coming up with the idea of how McClane kills Gabriel. In order to keep it a secret, the scene was not included in the film's shooting script.