Nina Hoss was always the first and only choice as Louise when Dennis Gansel wrote the script in 1999. She wanted the part from the get go. Karoline Herfurth had also been attached since the 90s but was too young to play Lena, the part Gansel wanted to give her. Instead he promised her the part of Nora. Due to the delay in production, however, Herfurth was old enough to play Lena when the film was finally green-lit.
According to Dennis Gansel, the vampires each represents a time in German history he thought where a high point Louise represents the lat 1700's, Charlotte the 1920's and the golden age of German films and Nora the 1990's after the fall of the Berlin wall.
Dennis Gansel got the idea for the movie while walking home to his apartment in Berlin after watching The Craft (1996). He came across a large abounded building and thought it was curious that such a place existed in Berlin. While walking home he began to fantasize about what could be going on in there. When he came home, his then girlfriend showed him some photos she had taken. There had been something wrong with the photos during the processing and the photos looked rather ghastly. And then the ideas came together in Gansel's head.
The inscription on the ceiling in the prison cell reads: "Sie befinden sich im Revier 38. Neukölln. Berlin. Deutschland. Europa. Erde." ("You are in station 38. Neukölln. Berlin. Germany. Europe. Earth.").
The scenes set in the hotel lobby were shot in the local district court of Berlin Mitte. The location was available for one night only and the team was still filming when the first prosecutors came to work.
At first the vampire teeth where complete bridges in the mouth which gave the actresses a undesirable lisp. Georg Korpas solved the problem by using glue-on teeth. Jennifer Ulrich actually forgot at times that she had fake teeth in her mouth.
During Lena's transformation scene, her hair was not supposed to grow out. Only the dye was to go away. The hair growing back was added since the shot was not effective enough. This made the shot very complicated to get right.
The song "Au clair de la lune" that Charlotte sings and is used as her theme is the first song ever recorded and also the first sound ever recorded. It was recorded in 1860 by Édouard-Léon Scott de Martinville.
Jochen Nickel had a larger role in an early cut. There was a whole subplot about Lena bribing him and due to the failed card theft she did not have enough money to pay him. In the final film all his dialogue but one line was cut, making him little more than a featured extra.
Dennis Gansel wanted to shoot the film in 2006 but financiers said no thus Gansel went on and made The Wave (2008) instead. As a side effect, many ideas that originated in "Wir sind die Nacht" also ended up in "Die Welle", giving the films thematic similarities. The most notable examples are the fact that both films feature a main character who has a single mother and does not care for them and the ending; both "Die Welle" and "Wir sind die Nacht" end with a character seeing something hidden from the audience. In "Die Welle", the character is frightened while in "Wir sind die Nacht" he is relived of what he sees.