Bela Lugosi received fourth billing even though he appears only near the end of the movie and only in one scene with Greta Garbo.
Greta Garbo had her misgivings about appearing in a comedy and was particularly nervous about the drunk scene, which she considered to be highly vulgar.
Although Greta Garbo's famous hat in the film was made by her regular costumier Adrian, it was in fact based on a sketch by Garbo herself.
According to Billy Wilder, Ernst Lubitsch contributed so much to the script that he and co-writers Charles Brackett and Walter Reisch took the most unusual step of petitioning the WGA to add Lubitsch to the screenplay credit. They were turned down.
The tagline "Garbo laughs!" came before the screenplay was written; the film was built around that single, now legendary, catch-phrase. This was itself a reference to another legendary advertising slogan about Greta Garbo. A famous leading lady of the silent film era, she made her first talking picture, Anna Christie (1930). That film was advertised, to great success, with the line "Garbo Talks!" When she made this comedy the "Garbo Laughs!" tagline resonated with her fans.