Gene Hackman turned down the film several times, but was ultimately convinced to sign on after a phone call by Director Tony Scott. Will Smith later signed on at a relative post-Independence Day (1996) bargain price because he wanted to work with Hackman.

The mark left on the mailbox to signal Brill is exactly how ex-C.I.A. official and traitor Aldrich Ames signalled the Soviets when he made a drop.

Will Smith improvised Dean's line about buying the lingerie for himself to try cross-dressing on the weekends. Smith has said it was difficult to restrain his comedic instincts during a dramatic role.

The NSA refused to cooperate with the production. Aerial footage of their headquarters in Fort Meade, Maryland had to be shot from public air space.

The film's technical advisor, Larry Cox, is a former National Security Agency official.

The storm drain car chase scene was shot in a large air duct tunnel below the four main bores of the Fort McHenry Road Tunnel in Baltimore, Maryland. Fort McHenry permits Interstate 95 to pass under Baltimore's harbor. The air duct is only accessible from the Tunnel's Administration Building by stairs and a small elevator, so the cars in the scene were chopped into several sections, taken three levels below, reassembled and painted. Once filming was complete they were disassembled once again and removed from the duct. The water was hosed in from a nearby sprinkler main.

Reynold's birthday is 9/11. Ironically, the "surveillance society" Hammersly mentions would eventually become the "Patriot Act" passed under the Bush administration post-9/11, only three years after this film was produced.

Tom Cruise was originally signed on to star in this film, but had to turn it down because he was still filming Eyes Wide Shut (1999).

The latitude and longitude given during the chase are the location of the real C.I.A. Headquarters in Langley, Virginia.

The satellites repeatedly send "CQ" in Morse code every time they're seen. "CQ" is ham radio shorthand for "Anybody out there want to chat?" ("Seek you.")

The portable video game system that Dean's son uses, and in which "the disc" won't work, is an NEC Turbo Express. It was a GameBoy competitor albeit with the ability to play TurboGrafx-16 games on a color screen. By the time this film premiered, it had faded into relative obscurity, making it the perfect piece of tech.

When Dean sees the article in the paper indicating that he's being investigated by the F.B.I., he says "They have NO Sullivan protection for this." He's referring to the Supreme Court case New York Times v. Sullivan, which set the standard for defamation cases brought against media companies.

Thomas Reynolds' birth date is given as 9-11-40. On September 11, 1940, Bell Labs researcher George Stibitz demonstrated the first remote operation (i.e., over a phone line) of a computer machine.

The building that served as Brill's workplace was originally a Dr. Pepper plant.

When Lyle (Hackman) is taking Dean (Smith) into the warehouse "office", one can see that it is a self-made Faraday Cage. One of the few constructs that completely shields those inside from sending or receiving electromagnetic signals.

Sir Sean Connery was considered for the role of Edward "Brill" Lyle.

The Ruby lingerie store is actually the doctored store front of Lambda Rising, a well-known gay bookstore on Connecticut Avenue in Washington, D.C.

Don Simpson and Jerry Bruckheimer began developing the story for the film in 1991.

When Brill accesses the National Security Administration's executive files to identify Reynolds, the very first photograph that flashes from the personnel files has the name "Buster, Ball" below it.

Will Smith turned down a role in another conspiracy thriller Snake Eyes (1998) to star in this film.

Mel Gibson was also considered for the role of Robert Clayton Dean.

Second-billed star Gene Hackman makes his first appearance at 55 minutes into the film.

The commercial on Zavitz's (Jason Lee's) television is for the EV1, GM's first and ill-fated electric car.

On the extended DVD version, Fiedler (Jack Black) goes into more sexually graphic detail about his attraction to the maid, and his overall attraction to women who don't shave in general.

Several times the location of a person or vehicle being tracked is given in degrees and minutes of latitude and longitude. Near Washington, D.C., this designates an area of about 1.02 square miles. Not quite as precise as shown.

Lisa Bonet portrays Will Smith's ex-girlfriend. Bonet's real life daughter, Zoƫ Kravitz, portrayed Will Smith's daughter in After Earth (2013).

Tony Scott initially turned down Jerry Bruckheimer's offer to direct the film.

Further connection to The Conversation (1974): The surveillance scene that takes place in Mount Vernon Square is very similar to the opening scene in The Conversation, which also features a conversation between a man and woman walking around the park.

The sound made by the bug sweepers used in the film is the same as the sound made by the sonar equipment in Crimson Tide (1995), also directed by Tony Scott. Gene Hackman, Jason Robards, Jr., and Lillo Brancato were in both films.

Sylvester Stallone was considered for a role.

Writing credits in the film's early promotional material read "Written by David Marconi and Aaron Sorkin and Henry Bean & Tony Gilroy".

The computer used by Daniel Leon Zavitz (Jason Lee) at his apartment to make a copy of the assassination's video on a removable media is a SUN Microsystems Ultra10 workstation.

George Clooney was considered for the lead role.

Hans Zimmer was the original composer for the film, but was eventually replaced by Trevor Rabin and Harry Gregson-Williams.

Robert's wife, Carla, makes reference to the fourth amendment, which is of/to the United States Constitution and part of a group of constitutional amendments known as the United States "Bill of Rights", a moniker carried over from the title of the proposal from which ten (initially and eleven eventually) of 27 amendments were ratified. The fourth amendment prohibits governments and civil authoritative bodies of/within the United States from searching or seizing anybody's person or belongings without reasonable suspicion and probable cause of the person's or the belonging's relevance to a specific crime; also requiring that warrants be detailed. This is related to the boundaries of privacy and is more or less related to privacy concerns in general, especially mass surveillance as a component of United States government's intelligence-gathering apparatus for foreign activity or that of military interest.

Will Smith and Jon Voight would later appear in, and score Oscar nominations for, Ali (2001).

When the NSA is raiding Brill's warehouse, one of the agents is wearing a thin plastic overcoat much like the coat Hackman's character wears through most of his earlier film, The Conversation.

Tom Sizemore played in a scene in True Romance (1993) in which multiple heavily armed groups of men faced each other at gunpoint in a small room with a shoot-out massacre as result. A similar scene appeared in Saving Private Ryan (1998), also featuring Sizemore. This movie contains another such scene, again featuring Sizemore.

Robert Clayton Dean tells his wife (played by Regina King), "You're the only woman for me. You and Janet Jackson." Regina King co-starred with Janet Jackson in Poetic Justice (1993).

Average Shot Length = ~2.4 seconds. Median Shot Length = ~2.2 seconds.

The opening scene indicates the conversation with and murder of Hammersley took place at Occuquan Park, Maryland. The scene was actually shot at the Loch Raven Fishing Center at 12101 Dulaney Valley Rd., Phoenix, MD 21131 just north of Towson. Occoquan Regional Park (note the spelling difference) is located south of D.C. in Virginia, not north of Baltimore.

Gene Hackman played another character named "Brill" in The Split (1968).

Boxing is on television in four separate scenes.

The film cast includes four Oscar winners: Gene Hackman, Jason Robards, Jr., Jon Voight, and Grant Heslov; and one Oscar nominee: Will Smith.

The Ecology Flag circa the first Earth Day can be seen on the truck of Daniel Zavitz as he drives away from retrieving the tape. In the shot where the man radio's the license plate number, the green and yellow flag can be seen on the upper left of the tailgate. The symbol was formed by taking the letters "e" and "o", taken from the words "environment" and "organism", and putting them in superposition, thereby forming a shape reminiscent of the Greek letter Theta. Zavitz also exclaims "Fuck a Duck" when he realizes what his hidden camera captures. He is a nature photographer monitoring the migratory patterns of Canadian geese.

The murder of Representative Hammersley (Jason Robards, Jr.) is copied to flash media by Daniel Zavitz (Jason Lee). The form factor of the media to which the recording is copied to is PCMCIA.

Gene Hackman's character's name (Brill) is very similar to his character in The Conversation (1974).

There are at least two sons of famous actors in this film, Jake Busey (son of Gary) and Scott Caan (son of James). You could probably also count Jason Robards, Jr., as his own father was a famous actor.

Tom Sizemore and Barry Pepper appeared in Saving Private Ryan (1998).

Gabriel Byrne and Loren Dean played major roles in The End of Violence (1997), another film that deals with the social perils of techno-surveillance.

Seth Green and Jack Black appeared in Airborne (1993).

Gene Hackman and Jon Voight were both considered to play U.S. Marshal Samuel Gerard in The Fugitive (1993), which went to Tommy Lee Jones, who also worked with Will Smith on the Men in Black trilogy. Both Hackman and Voight have also worked with The Fugitive (1993) Director Andrew Davis on movies like Holes (2003) and The Package (1989), which also co-starred Tommy Lee Jones.

Jon Voight and Tom Sizemore appeared in Heat (1995) and Pearl Harbor (2001).

Jason Robards, Jr. and Jon Voight both played the role of President Franklin D. Roosevelt in two separate movies. Robards in F.D.R.: The Last Year (1980), and Voight in Pearl Harbor (2001).

Seth Green and Jason Lee appeared on My Name Is Earl (2005).

Jamie Kennedy and Scott Caan appeared in Boiler Room (2000).

Will Smith and Jason Lee appeared in Jersey Girl (2004).

The NSA conference room set with the wood paneling strongly resembles the CIA conference room of "Spy Games." The twittering sound over the location titles also sounds very similar to that of "Spy Games."

Dan Butler played N.S.A. Director Shaffer, pronounced like "Schaefer", which is the German name for an Alsacian sheep dog. On Frasier (1993), he played a character named "Bulldog".

The last name "Banks" is a common thread. Will Smith played on The Fresh Prince of Bel-Air (1990) (last name of his family is Banks) and his love interest (former girlfriend) in this film is Rachel Banks, played by Lisa Bonet.

In the movie, Dean uses the nickname "E" for his son Eric, the same nickname used for the character of Eric Murphy in Entourage (2004). Seth Green, Jamie Kennedy, Scott Caan, and Paul Herman appeared on the show. Aaron Sorkin, who wrote the film uncredited, also appeared on the show.

Jason Lee and Loren Dean appeared in Mumford (1999).

Will Smith & James Le Gros appeared in Where The Day Takes You (1992).

Laura Cayouette, who plays Christa, the Representative's aid, was born in Laurel, Maryland, which neighbors Fort Meade, where the N.S.A. is headquartered.

The picture of a younger Gene Hackman shown in a white shirt and tie, supposedly from his N.S.A. file, was actually taken from The Conversation (1974). Hackman's character Brill, closely resembles his "Conversation" character, Harry Caul. In The Conversation (1974), Harry Caul, like Brill, is a paranoid surveillance expert who has his workplace in an industrial warehouse. Also, Brill wears the same translucent raincoat worn by Harry Caul in the previous film. In The Conversation (1974), Harry Caul (like Robert Dean in this film) is pressured to hand over a tape (albiet an audio tape) that has evidence of a murder conspiracy. At the end of The Conversation (1974), Caul demolishes his apartment when he thinks people who have been observing him might be coming for him. (It's been suggested by more than one film critic that Brill could actually be an older Harry Caul, living under a pseudonym.)

Representative Hammersley and Rachel Banks are killed after they say the same line: "This conversation is over." Hammersley almost immediately, and Rachel by the next morning.

The newspaper article that clears the main character of all charges at the end of the film is signed by Kilian Kerwin, who is not credited in this movie, but has worked as assistant to Director Tony Scott.

Gene Hackman doesn't appear until 57 minutes into the film.