It took four months to assemble and combine archive footage of past American presidents from Franklin D. Roosevelt to George W. Bush to create the televised warning from Gabriel. The goal was to create a video representation of a ransom note.

The elevator shaft sequence was not in the film's script when Len Wiseman was hired as director. Wiseman added it because he associated elevator shafts and claustrophobic spaces with Die Hard (1988).

Kevin Smith rewrote the lines for his Warlock character. Bruce Willis thought the rewrite was too funny and did not follow the serious mood of the movie. Smith then rewrote the part to what Willis requested.

The only Die Hard movie to take place over the course of more than one day.

The stunt featuring McClane driving a police car into a helicopter took three weeks to rehearse. The shot was accomplished by suspending the helicopter in the air with cables and combining two separate shots; one of the stuntman leaping from the helicopter and one of the car colliding with it. CGI was then used to delete the support cables and add rotor blades.

Bruce Willis' stunt double, Larry Rippenkroeger, was seriously injured when he fell 25 feet to the pavement. He suffered broken bones in his face and fractures in both wrists. Production was temporarily shut down. Willis picked up the tab at area hotels for Larry's parents and visited him numerous times at the hospital. Larry also doubles for James Caan in his television series, Las Vegas (2003). Caan came and visited Larry in the hospital and joked around for over an hour. Larry told his parents he was glad when Caan left because he hurt so bad from laughing at his jokes.

According to Bruce Willis and director Len Wiseman in the DVD commentary, the story originally involved McClane's son, Jack. Originally, he was supposed to be the computer hacker John has to deliver to the FBI. Eventually that idea was dropped and the hacker became the Matt Farrell character. It was then decided to bring in his daughter Lucy to keep up the series theme of McClane always having a personal stake in what happens in the story.

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 (1990) 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?" Len Wiseman dubbed the last part of this line ("Gonna stop me"), imitating the voice of Bruce Willis.

When filming the scenes of John walking through the corridors talking to Gabriel on the two-way, there were no written lines of dialogue for Bruce Willis, according to Len Wiseman on the DVD commentary. So what they did on set was have Willis hold the two-way up to his mouth and speak gibberish so it looks like he's talking to Gabriel. If you'll notice, there are a couple of times where the two-way isn't all the way up to Willis' face and you can see his mouth doesn't match the dialogue being spoken.

This film addresses the apparent continuity error in earlier installments - McClane is afraid of flying in Die Hard (1988) and Die Hard 2 (1990), but not Die Hard with a Vengeance (1995). Here, he explains that he took flying lessons in order to "face his fears."

In the elevator shaft scene, where Mai Lihn swings on the wire, and flies into the truck and hits McClane, the stunt double accidentally cut Bruce Willis' eyebrow with her spiked heel, and according to Len Wiseman in the DVD commentary, she jabbed Willis hard enough that when medics examined the injury, the brow bone was exposed.

French actor and martial artist Cyril Raffaelli, who plays Rand, does his stunts almost without special effects and wires.

In the opening credits, when Kevin Smith's name comes on the screen, the "m" in Smith disappears and you see "Sith" for a few seconds, paying homage to Kevin Smith's love of all things Star Wars, which also reflects in his character in the movie.

When McClane throws Russo down the stairs, the stuntman landed so hard that his impact dented one of the thick metal steps.

When released on DVD on November 20, 2007 in the U.S. and Canada, it became the first DVD ever to be packaged with a digital copy.

The plot point of McClane having to rescue a kidnapped Lucy was carried over from a rejected script for Die Hard with a Vengeance (1995).

The bad guy, Thomas Gabriel, points a gun at McClane and declares, "On your tombstone it will say 'Always in the wrong place at the wrong time'." "John McClane is back in the wrong place at the wrong time!" was a tagline used for Die Hard 2 (1990), and the character is told that he is "the wrong guy in the wrong place at the wrong time!" by Major Grant in that movie.

The phrase "Live free or die" is from a toast written by the revolutionary soldier General John Stark. The full phrase is "Live free or die: Death is not the worst of evils".

The first sequel in the series where no character mentions John McClane's encounter at the Nakatomi Plaza in Los Angeles, in Die Hard (1988). However, visual references to Nakatomi Plaza are seen while Thomas Gabriel is looking at John McClane's dossier.

The script was not originally written to be a 'Die Hard' sequel.

In addition to the 'Agent Johnson' reference, several other elements from the first Die Hard (1988) 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, (heard in its uncensored glory in the unrated version).

Each film in the Die Hard series contains a key scene involving an elevator.

Scott Speedman was Len Wiseman's first choice for the role of Matt Farrell whereas Ben Affleck was Bruce Willis' first choice for the role. Willis wanted Affleck in order to recreate the chemistry between two characters previously accomplished in Armageddon (1998)

The movie was filmed in two versions, one for an R rating and the other for a PG-13 rating. It was edited to a PG-13 rating for commercial reasons, making it the first film in the series not rated R upon its theatrical release. The DVD contains the theatrical version and the unrated version. The unrated version restores much of the profanity and violence that was cut for the PG-13 version, making the film the equivalent of an R rating.

The first Die Hard film that is set in multiple locations (New Jersey, Washington, D.C., West Virginia, and Baltimore). The first three were all set in and around (or above) primarily one location throughout most of the movies.

This is the first Die Hard film without the music of film composer Michael Kamen, who died in 2003. Portions of Kamen's previous "Die Hard" scores, however, were incorporated into the score by Marco Beltrami.

John McClane's date of birth is revealed as May 23, 1955 when Thomas Gabriel looks at his dossier.

The name "Tovarek", which Mai Lihn uses as an FBI agent, is a Polish word and one of its meanings is "hot chick" (the correct Polish word is "towarek", but it's pronounced like this). Tara Tovarek is also the name of producer Michael Fottrell's assistant.

The first Die Hard film where no reference is made to Christmas.

A single frame shot of director Len Wiseman's then-wife Kate Beckinsale is spliced into the opening credits, when the van is outside the exploding house.

The Terminator action figure in Matt's apartment is a nod to executive producer William Wisher, Jr. and composer Marco Beltrami. Wisher co-wrote and appeared in The Terminator (1984) and Terminator 2: Judgment Day (1991), and Beltrami composed the score for Terminator 3: Rise of the Machines (2003).

When Gabriel is talking to McClane over the phone and pulling up his information on the computer, Bonnie Bedelia makes a cameo appearance in the form of her character Holly McClane's driver's license photo. The photo appears as though it may be either a publicity shot from a prior "Die Hard" film or a still photo (i.e. family portrait) from one of the movies.

While in early development with a script that was eventually discarded, the movie had been given the subtitle "Tears of the Sun". Bruce Willis told the studio he would commit to a Die Hard 4 if he could use the title for Tears of the Sun (2003). The "Tears of the Sun" script was written by Alan B. McElroy in 1990's but it wasn't originally written as Die Hard 4, instead it was about group of people who go to Amazon to set up a radio relay station but then their plane gets stolen and they are captured by drug dealers to work as slaves in their mine, however they manage to escape into the jungle and end up having to run and fight for their lives.

The opening scene between McClane and Lucy was filmed on the campus of the University of Southern California in Los Angeles. The building that serves as Lucy's dormitory is actually Doheny Library.

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.

The first film in the series where the antagonist does not use a fake accent. In Die Hard (1988), Hans Gruber faked an American accent to fool McClane; in Die Hard 2 (1990), Colonel Stuart fakes a Midwestern accent while guiding an airline pilot into crashing into the ground; and in Die Hard with a Vengeance (1995), Simon fakes an American accent while posing as a city engineer.

On the DVD commentary, director Len Wiseman discusses the "back yard Die Hard (1988)" he shot when he was younger. At least one of the shots from it was used in this film, and Wiseman acted it out for Bruce Willis during filming so that Willis could duplicate it.

The fighter jet is a F-35 fighter (sometimes called JSF or Joint Strike Fighter). At the time of the movie this type of fighter jet wasn't operational yet, the very first F-35 maiden flight was in June 2008. In this film the variant is an F-35B which can hover and take off or land vertically as depicted.

When McClane is driving in Jersey and talking to the chief captain of Camden, the guy's name is Wiseman, same name as the director, Len Wiseman, although pronounced 'Wheezeman', as this was how most crew-members thought his name should be pronounced. The voice is that of the director himself.

Each day of shooting cost an average of $375,000.

The movie's title, "Live Free or Die Hard", is a reference to New Hampshire's state motto "Live Free or Die". Consequently, the New Hampshire state film office received several phone calls asking where in the state the movie was filmed.

The car that is stolen in the film by McClane and Farrell is a 2006 E60 BMW 5 series, which was chosen due to a poll that found that people wanted films that had more BMWs in it. The main reason given was that the alternatives (Audis and Mercedes-Benzes) were too common and not bold and imposing enough to go with the characters in the film. The particular BMW model (5 series) was chosen because the director, Len Wiseman, found "the 3 series too common, the 7 series too uptight and every other car either too feminine or compensating for a midlife crisis... Everything McClane isn't, yet".

One of Matt Farrell's hacker pals is named Clay, a clear nod to the alias Hans Grüber uses when he accidentally stumbles across McClane unarmed whilst searching for the detonators at the Nakotomi plaza in Die Hard (1988). The name Grüber uses to fool McClane was Bill Clay.

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, "Gennero". A similar argument takes place in Die Hard (1988), 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", which is misspelled.

All the IP-addresses shown in the movie are legal ones. However, most start with either 10, 172.16 or 192.168. Those numbers are reserved for local traffic only. At 02:04, one of the hackers transfers data with scp to 202.218.154.52, which is owned by a Japanese company.

Justin Timberlake was in talks to play John McClane's son.

So far, this is the only film that Len Wiseman directed that didn't star Kate Beckinsale or Bill Nighy.

The first film in the Die Hard series not to be shot in the anamorphic Panavision process. This film was shot in Super 35 to save money with visual effects.

This is the only installment of the series where John McClane doesn't carry his Beretta 92FS. Instead he carries a SIG-Sauer P220R. The 92FS does appear in the film, wielded by one of Gabriel's henchmen.

Executive producer William Wisher, Jr., co-writer of The Terminator (1984) and Terminator 2: Judgment Day (1991), made uncredited contributions to the script.

This is one of a few movies where Bruce Willis character has a daughter who calls him by his first name due to a troubled relationship. Others include; Armageddon and The Last Boy Scout.

A list of the United States Presidents used in the making of Thomas Gabriel's (Timothy Olyphant) "video package" - George W. Bush (R) {2001-2009}, Bill Clinton (D) {1993-2001}, Ronald Reagan (R) {1981-1989}, Jimmy Carter (D) {1977-1981}, Gerald Ford (R) {1974-1977}, Richard Nixon (R) {1969-1974}, Lyndon B. Johnson/Lyndon B. Johnson (D) {1963-1969}, John F. Kennedy (D) {1961-1963}, Dwight D. Eisenhower (R) {1953-1961}, and Franklin D. Roosevelt (D) {1933-1945}.

Samuel L. Jackson was at one point rumored to be reprising his role of Zeus Carver, (from Die Hard With a Vengeance (1995)) for this movie.

The screen to the far left of all of Warlock's hacking screens has the auction website eBay open with a Boba Fett action figure being watched. Later, in Warlock's basement sanctuary we see a large cardboard cut-out of Boba Fett, reflecting Kevin Smith's Star Wars fandom.

According to the files that Thomas Gabriel pulls up on Holly Gennero, her driver's license records list her address as the fictitious 9975 Geyser Way East, San Francisco, California, 9424- (the smaller picture on her license obscures the final ZIP code digit).

The French title translates as "Die Hard 4.0: Return to Hell".

Marks the fourth successive film in the Die Hard franchise where John McClane talks to the main villain via walkie talkie.

Kal Penn and Brad Renfro both auditioned for the role of Matt before it went to Justin Long.

Britney Spears and Taylor Fry auditioned for the role of Lucy McClane.

This is the highest grossing Die Hard movie.

Because of Len Wiseman and Bruce Willis' insistence on using practical effects as much as possible instead of an over-reliance on CGI, post-production on the film only took 16 weeks instead of the usual 26.

The filming title used by the crew and to mark locations was "Reset".

This is the first Die Hard film not to have an R rating. Bruce Willis was not happy about the studio's decision to have a PG-13 movie but later admitted that he loved the finished result, even preferring it to the first in the series.

Timothy Olyphant filmed his role in just three weeks.

Both Len Wiseman and Bruce Willis openly admitted to preferring the film's international title, "Die Hard 4.0".

Bruce Willis had to be briefly hospitalized when a stunt double accidentally kicked him in the face, lacerating him just above the eye. He required stitches, though he dismissed the injury as being no big deal at the time.

The exterior of the Social Security Administration building in Woodlawn, Maryland, is Diamond Ranch High School, located in Pomona, California. In the original Die Hard, John McClane tells his wife he is staying with his friend Cappy Roberts in Pomona, California.

Jessica Simpson auditioned unsuccessfully for the role of Bruce Willis' daughter. She can be seen going to and then coming from the audition in Newlyweds: Nick & Jessica: Mismatched Threesome (2004).

The first Die Hard film where John McClane doesn't go face-to-face with his antagonist before going into a final combat in the ending.

There are over 200 visual effects in the film.

There is another Special Agent Johnson in this movie. In the original Die Hard there was also a Special Agent Johnson and Agent Johnson who were "not related".

The character portrayed by Maggie Q impersonates an FBI agent, Maggie Q would later portray FBI Agent Hannah Wells in Designated Survivor (2016-2018).

When McClane is driving in Jersey and talking to the Chief Captain of Camden, the guy's name is Len Wiseman - the same name as the director.

Rob Huebel auditioned for the role of Matt Farrell.

The three top billed cast members, Bruce Willis, Justin Long and Timothy Olyphant, all have connections to Jennifer Aniston, Bruce played in a few episodes, season six, of "Friends" ('94-'04), as Rachel's boyfriend; Justin played her assistant in "The Break Up" (2006); and Timothy was the lead guitar player in the band she managed in the film "Rock Star" (2001).

Eli Roth turned this movie down to do Hostel Part II.

The 12th highest grossing film of 2007.

Tony Jaa was rumored for a role in the film.

Rumer Willis was considered to play McClane's daughter.

Maggie Q stars in this movie and Designated Survivor, both of which depict the physical destruction of the Capitol Building.

The radioplay TKKG - Folge 183: Blindgänger im Villenviertel makes many references to the Die Hard movies, including the character name John McClane.

Justin Long said he didn't want to be accessory to Armageddon. Bruce Willis starred in the film Armageddon.

John McClane (Bruce Willis) calls Freddy (Kevin Smith) a "dump truck". In the previous Die Hard movie, "Die Hard With A Vengeance", dump trucks are featured prominently as part of the villain's plan.

In Warlock's basement is an arcade game Asteroids. Bruce Willis starred in the film Armageddon, which involved him mounting a mission to save the Earth from a rogue asteroid.

Len Wiseman: Pilot of the F35 jet.

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.

In the scene where all the lights turn green to cause an accident, a scene from The Italian Job (2003) is shown on the monitors watching the crash. In the original Italian Job, the robbers reprogrammed all the traffic lights to go haywire to aid their robbery.

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.

When Lucy informs John McClane that there are five villains left, she actually miscounts because there are six: Thomas Gabriel, Trey, Emerson, Rand, the truck driver (Robinson) and the one that would later guard her in the Hazmat truck. This is probably the reason, that after killing four of them, McClane was not aware of Emerson's presence in the warehouse at the end, until he is shot by him. This could be in reference to Die Hard 2 (1990) when after only killing five men (Cochrane, O'Reilly, Mulkey, Sheldon and Thompson), he says there are six dead bad guys.

When McClane shoots Gabriel through his own right shoulder, the bullet should have entered Gabriel's right chest since he was standing directly behind him. However, when Gabriel falls down the bullet hole is in his left chest.

Kevin Smith and Timothy Olyphant both appear in the movie Catch and Release one year prior.