Anne Fontaine originally met with Agata Kulesza in Poland because she was an admirer of her work, but told her that she didn't wish to cast her as the Mother Superior since she thought her too sexy for the role. The actress laughed and asked the director if she could put on a veil and read an extract for a Polish work. Once she did, Fontaine decided to give her the part.
Director Anne Fontaine went on two retreats in Benedictine communities in preparation for the film, first as an observer and second as a novice.
Based on the true story of Madeleine Pauliac, renamed Mathilde Beaulieu in the film, during her time working as a doctor in Poland. The story was brought to the attention of producers by Pauliac's nephew, Philippe Maynial, who had her diary.