UFA insisted on the film being very cheap in the making as Fritz Lang's previous film Metropolis (1927) had brought the studio to near bankruptcy. Lang therefore choose to do most of the shots in narrow settings with lots of close ups, as no big sets had to be built up for that way of filming. Fortunately "Spione" became a huge success.
Gerda Maurus, whose film-debut "Spione" was, and who met Fritz Lang for the first time here, later had a long relationship with the director, eventually causing his divorce from Thea von Harbou, who at the time was his wife and remained his regular co-author up until Das Testament des Dr. Mabuse (1933), Lang's last German film before emigration to the U.S..
Fritz Lang consciously choose to introduce Willy Fritsch as a scruffy homeless person, for Fritsch was most known from his previous films as the elegant gentleman he later becomes in this movie as well.
Director Fritz Lang was so obsessed with realism that in the scene where Agent 326 saves Sonya from a bullet, Lang used a real gun loaded with real bullets shooting at a glass plate directly behind the actors. Lang felt he need real danger so the actors act out the danger of the situation. Lang was convinced the actors had to be afraid during the shooting scene to make the audience afraid. Thankfully, no one was hurt.