17 days before shooting was to commence in Morocco, none of the characters had been cast. The production crew made an announcement in the nearest town via television and radio and in the mosques that actors were needed. Within the next 24 hours, over 200 people showed up hoping to participate. Almost all of them are in the final cut of the film, both as principal characters and as extras.
The scene where Chieko (Rinko Kikuchi) and her father are in the car together was shot without filming permission from the city due to slow Japanese bureaucratic procedures. The crew created "man-made" busy traffic, and began shooting the scene. Later the police started chasing them while still shooting the scene.
Brad Pitt gave up one of the starring roles in The Departed - Il bene e il male (2006) (a film he co-produced) in order to participate in this film, as he's a longtime fan of Alejandro G. Iñárritu's films.
Almost all of the film, even the driving scenes, was shot using a hand-held camera.
Since each story was filmed at different times and on different continents, some of the cast members never met their counterparts until the film's premiere.