Once the screenplay was completed, it was sent to the relatives of the monks to receive their approval.
In researching the screenplay, director Xavier Beauvois spent six days living at the Tamie Abbey in Savoie. All the actors were required to do the same as well.
The actors trained for a month under Francois Polgar, the former assistant director of the Paris Opera choir. This helped them sound more authentic when it came to singing Gregorian and Cistercian chants. Of the actors, only Lambert Wilson had any previous experience of singing, having performed in several one-man shows.
When the film was released in the United Kingdom, it was only shown in 16 cinemas. Nevertheless it still managed to crack the top 15 films of the week.