According to an interview that screenwriter Lawrence Wright gave to CBS in 2007, the film was a box-office failure upon its theatrical release, "but it was the most-rented movie in America after 9/11." Wright also claimed that the initial release bombed because "Muslim and Arab protesters picketed the theaters. They were furious at being stereotyped as terrorists."
Bruce Willis was welcomed to the Pentagon where he received a crash course in briefings and information that, while unclassified, did give him a sense of what General Devereaux would deal with, both in general, and in the event of a major national crisis.
In several scenes, General William Devereaux is seen not wearing his U.S. Army uniform, instead he's seen wearing an ordinary suit. It is revealed that General Devereaux is actually holding a position in the President's cabinet while retaining his Army commission as a Major General, possibly National Security Advisor, or White House Chief of Staff. This resembled Alexander Haig, who was Richard Nixon's Deputy Assistant to the President for National Security Affairs and later White House Chief of Staff, while retaining his General rank in the Army, or Colin Powell, who was Ronald Reagan's National Security Advisor, while also retaining his General rank in the Army, and later known as "political General".
Two early possible titles for this film were "Holy War" and "Against All Enemies". The former title was nixed after it was agreed by all principals to be much too incendiary, and the latter was used for a while before the studio decided "The Siege" was a more apt, stronger title. Ironically, "Against All Enemies" would later become the title of a post-9/11 nonfiction book that itself is a future film project.
While negotiating with the bus bombers, Hubbard offers to exchange himself for the hostages. In Ricochet (1991), Denzel Washington's character makes the same offer while negotiating with another criminal holding a woman hostage.
During the period when this movie was being filmed (including in various locations around New York City), Donna Hanover (who played the District Attorney) was married to Rudolph Giuliani, the then-mayor of New York City.
The trivia item below may give away important plot points.
Annette Bening said that an early draft of the script concerned her because she felt there was material in it that would be offensive to Jewish Americans. She was not specific about what this meant, and in the end the movie had no controversial scenes involving Jews at all (one of the top FBI agents is Jewish and dies with hundreds of his colleagues in a terrorist bombing, and some of the information about the terrorists comes from Israeli intelligence).