Danish actress Iben Hjejle was originally cast as the German woman Birgit and was signed on. When the film's German financiers discovered that a Dane had been cast as a German, they made sure a German actress, Anneke Kim Sarnau, was cast instead.
The character Tessa Quayle was based on famous social activist and charity worker Yvette Pierpaoli, who was killed in 1999 with two other social workers when their truck crashed in Albania. The book was written in her memory.
Marcus Lorbeer (played by Pete Postlethwaite) wears a baseball cap that has a yellow equal sign (=) inside a blue square. This is the logo of Human Rights Campaign, a non-profit organization that lobbies for equal rights based upon sexual orientation and gender identity. It is the largest gay, lesbian, bisexual, and transgender advocacy organization in the United States.
The scene where Tessa (Rachel Weisz) walks through the slum, numerous children ask her "How are you?" and she responds "I'm fine, how are you?" was unscripted. The children are actual children who live in Kibera and not extras.
Producer Simon Channing Williams bought the rights of the book in advance before its release in 2001 with the intention of bringing it to screen. In order to get John le Carré's permission to do so, he wrote a letter to Le Carre's attorney Michael Rudell informing him of the intention and flew to New York on the same day. This is the second time that Le Carre has worked on the screenplay of a film; the first was The Tailor of Panama (2001). To ensure total accuracy, Nairobi-based molecular biologist Bonnie Dunbar was brought in as the film's consultant.
The filmmakers installed water tanks, a new bridge and a classroom in Kibera, the slum in which the film was shot. They also built a secondary school in the desert of northern Kenya where the final scenes were photographed.
The trivia items below may give away important plot points.
At the eulogy for Justin, Pellegrin quotes this line: "Nothing in his life became him like the leaving it." That quote is taken from the beginning of Macbeth: [King Duncan: Is execution done on Cawdor? Are not those in commission yet return'd? Malcolm: My liege, they are not yet come back. But I have spoke With one that saw him die; who did report That very frankly he confessed his treasons, Implor'd your Highness' pardon, and set forth A deep repentance. Nothing in his life Became him like the leaving it.] In Macbeth, the "him" referred to is a traitor who had been executed for betraying his king. Justin has been murdered for doing the same thing. Pellegrin's gall in using this quote is amazing, especially when it seems fairly clear he ordered the hit in the first place.
In a deleted scene, seen on DVD extras, Swedish actress Pernilla August plays an employee at the Canadian company that was responsible for the drug research. Her character gave Justin Quayle information that led him to Dr. Lorbeer. Moments after doing this, she is killed in a mysterious hit-and-run car accident.