Some of the dialogue comes directly from recordings made by the Stasi, the East German secret police.
Edgar Ramírez put on 35 pounds over the duration of filming to show Carlos's physical deterioration leading up to the time of his capture.
According to Edgar Ramírez, they shot in over 200 locations.
Olivier Assayas was initially not interested in the project as it seemed "too crazy and too complicated". However, his opinion swayed when he realized that he could make a film dealing with recent history and real people.