To live the role, Viggo Mortensen would sleep in his clothes and deliberately starve himself. At one point, he was thrown out of a shop in Pittsburgh, because they thought he was a homeless man.
Director John Hillcoat filmed the soft drink vending machine scene with Man and Boy several times, each with a different brand beverage, out of concern that Coca-Cola executives would not want their product to appear in this movie. A telephone call, from Viggo Mortensen to the President of Coca-Cola, secured permission for a can of Coca-Cola to appear, consistent with the source novel.
Viggo Mortensen nearly turned down the role of Man, because he had planned a break from film work. After completing his work as Man, Mortensen took roughly two years off from acting.
During a preview Q&A screening in London, John Hillcoat revealed that Kodi Smit-McPhee won the role of "The Boy", partly due to an audition tape sent in by Kodi's father that showed them re-enacting the scene where the father shows the boy how to kill himself, by placing a pistol in his mouth.
The ocean scene was Lake Erie.