Director Sam Mendes designed the two girls' look to change over the course of the film, with Thora Birch gradually using less makeup and Mena Suvari gradually using more, to emphasize his view of their shifting perceptions of themselves.
When Lester throws the asparagus, he was supposed to throw it on the floor. The reactions of Annette Bening and Thora Birch are genuine.
According to his Oscar speech, screenwriter Alan Ball was sitting at the World Trade Center plaza when he saw a paper bag floating in the wind and was inspired by it to write the film, which was originally conceived as a stage play.
Kevin Spacey improvised everything he does in the car while his character is stoned and singing to "American Woman."
When Lester masturbates in bed beside Carolyn, Sir Sam Mendes asked Kevin Spacey to improvise several euphemisms for the act for each take. Mendes said, "I wanted that not just because it was funny [...] but because I didn't want it to seem rehearsed. I wanted it to seem like he was blurting it out of his mouth without thinking. [Spacey] is so in control - I wanted him to break through." Spacey obliged, eventually coming up with 35 phrases, but Annette Bening could not always keep a straight face, which meant the scene had to be shot 10 times.