Cate Blanchett was originally signed to play the role of Anna, but due to her second pregnancy she had to drop out of the film.
Clive Owen played the role of Dan in the original stage production.
At the beginning of filming, Natalie Portman gave 'Julia Roberts' a necklace that said "cunt" in honor of their characters' foul mouths. At the end of filming, Julia Roberts gave Natalie Portman a necklace that said "lil' cunt".
The opera that Dan and Anna are late for and you can hear in the background is "Cosi Fan Tutte" - this also deals with themes of two couples who swap partners.
The park Dan and Alice walk through is Postman's Park in London, near St Paul's Cathedral.
The trailer includes several things that are not in the film.
different lighting when Anna and Dan kiss
shots of the driver of the car that hits Alice
a shot of Larry and Anna getting dressed
Larry telling Alice, "You women don't understand the territory, because you are the territory"
Anna asking Dan, "Why did you swear eternal love when all you wanted was excitement? Love bores you." Dan responds, "No, it disappoints me."
Anna's exhibition is the only time all four characters are in the same room.
'Julia Roberts' ' character, Anna, was originally played on stage by Natasha Richardson.
When we last see her in bed, 'Julia Roberts' 's character, Anna, is reading Private Eye.
Damien Rice, who sings the song "Blower's Daughter" on the film's soundtrack, Recorded a song for the movie also called "Closer" - but the song wasn't finished in time for the movies release.
A segment of dialog from the movie was used for the titles of two Panic! at the Disco songs: "Lying is the Most Fun A Girl Can Have Without Taking Her Clothes Off" and "But It's Better If You Do."
The photograph of an elderly couple which appears before Alice is photographed by Anna, and which appears also in Anna's exhibition, is a photograph of British philosophers Peter Geach and G. E. M. Anscombe.