The film was very much improvised by the actors and actresses, who used the screenplay only as a guide. They spent a great amount of their time in character, and the movie was shot almost entirely in sequence.
All songs were recorded live rather than being prerecorded in a studio.
Barbara Harris's singing ability had won her awards on Broadway, but film audiences knew her only as an actress. As such, Robert Altman did not want the audience to hear Harris sing until the last scene of the film so they would be surprised that a seemingly talentless dreamer actually had the stuff of stardom.
Each actor and actress was required to write and perform his or her own songs for the movie.
In the opening sequence, the character played by Henry Gibson demanded that his piano player be replaced by the "Pig". At that time in Nashville, one of the most in-demand session players was a blind pianist named Hargus "Pig" Robbins. The man playing the piano in that scene is Richard Baskin, the Music Supervisor on the film.