British author Christopher Isherwood, who created the character of Sally Bowles in his short story "Goodbye to Berlin", enjoyed the attention the movie brought to his career, but felt Liza Minnelli was too talented for the role. According to him, Sally, an amateur talent who lived under the delusion she had star quality, was the antithesis of "Judy Garland's daughter".
The character of Sally Bowles was based on Jean Ross, an aspiring actress, singer, and writer, who lived a colorful life. She was reportedly unhappy with Isherwood's portrayal of her as apolitical, and even slightly antisemitic. She was a member of the Communist Party, and may have been in Germany as an agent of the Comintern. She was also married for a time to Claud Cockburn, the father of journalist Alexander Cockburn, who described her as "a gentle, cultivated, and very beautiful woman, not a bit like the vulgar vamp displayed by Lisa Minnelli."
In an interview given at the time of the film's release, Liza Minnelli said you could tell she was the star of the cabaret in which the movie is set, because she's the only performer with shaved armpits.
"Tomorrow Belongs to Me" was written by John Kander and Fred Ebb in the style of a traditional German song, sung by the Nazi youth in the movie, to stir up patriotism for the "fatherland". It has often been mistaken for a genuine "Nazi anthem" and has led to the songwriters being accused of anti-Semitism. This would be most surprising, as they are, in fact, Jewish (This fact has not stopped openly racist and anti-Semitic rock groups, like Skrewdriver, from recording the song and performing it at White Power rallies). It is also the only song sung outside of the cabaret setting to survive the transition from stage to film.
The strange woman appearing at the beginning of the movie sitting in the back of the Kit-Kat Club holding a cigarette is based on the painting "Portrait of Journalist, Sylvia Von Harden" by German Expressionist painter Otto Dix.
Brian expresses surprise that Sally Bowles is an American, a sly reference to the fact that, in the musical on which the movie is based, Sally is British. In the original Christopher Isherwood books (which are semi-Autobiographical) both Sally and Brian were English.
The original Broadway production of "Cabaret" opened at the Broadhurst Theater on November 2, 1966, ran for 1165 performances and won the 1967 Tony Award for the Best Musical. Joel Grey recreates his role in the movie for which the won the 1967 Tony Award for Best Featured Actor in a Musical. He later won the Academy Award for Best Supporting Actor for this film, making him one of a handful actors to have won both a Tony and Oscar for the same role, a feat most recently achieved by Viola Davis for Fences (2016).
Instead of writing a new ballad for the film, John Kander and Fred Ebb were persuaded by Liza Minnelli (and later, Bob Fosse) to use a song from their trunk - "Maybe This Time", a tune Liza had recorded for her very first album. Fosse wasn't initially a fan of the song, but changed his mind after deciding on how to stage it (in the empty nightclub). Minnelli has said that Fred Ebb jokingly blamed her for the loss of an extra Oscar nomination in the Best Original Song category for her desire to sing a previously-written title.
In a 1972 interview with Dick Cavett, Liza Minnelli said that she learned Sally Bowles was a real person, so she put personal ads in newspapers in a futile attempt to meet her. Presumably Minnelli was unaware at the time that Sally Bowles wasn't her real name (the character was based on Jean Ross).
There is much speculation about the identity of the singer of "Tomorrow Belongs to Me". Apparently, Bob Fosse's biography states that the song was recorded for the film by Broadway actor/singer called Mark Lambert. This actor is said to have refused to dye his hair blond; so a German extra (the "Nazi youth") stood in for him on camera.
During the opening number "Willkommen", the Master of Ceremonies says, "Outside it is windy, but inside it is so hot." In the stage musical, he says that outside it is winter. "Winter" was changed to "windy" in the film so that exteriors could be shot in warm, sunny weather. That way, audiences wouldn't question the unusually mild German winter weather.
Five songs from the original Broadway production did not make it into the movie as "performed" songs, but appear as background music. When Brian arrives, Sally prepares two Prairie Oysters and puts on a record, which turns out to be "Don't Tell Mama". When Sally tries to seduce Brian and she brings in the gramophone, the song is "It Couldn't Please Me More". The same song, once again on gramophone, reappears when Sally is packing for Africa. In the parlor as Sally prepares to leave for dinner with her father, the song being played on the piano is "Married". This song makes a reprise when Sally and Brian talk about getting married, this time on the gramophone in German ("Heiraten") sung by Greta Keller. The German version is also heard in the park and at the train station. When Max, Brian, and Sally have lunch at the fancy restaurant, a small ensemble is playing "Sitting Pretty", which is also heard on the gramophone at Max's estate, when they are dancing. When Brian and Fritz walk into the parlor together and the other tenants are talking about the Nazis, the background music, faint and barely recognizable, is the song "So What."
Two songs that did not appear in the musical were written specifically for the film. Liza Minelli's famous first performance in the film, "Mein Heir," and Minelli and Joel Grey's duet "Money, Money. "Maybe This Time" also did not appear in the musical, but was written by Minnelli before the film and she suggested to put it in. She felt it would fit at the part where Bob Fosee, Fred Ebb and John Kander were initially going to create another original song for (where the song appears in the film). Fosse initially didn't like the song, but changed his mind after seeing the setting for the song in the film, the empty Cabaret. Fosse later joked that Minelli lost them out on another Best Original Song nomination.