While the soloists and actors usually receive the most attention in any play or musical, it is often the hard work of the music director that makes the production successful. Many people may be aware that the basic function of the music director is to conduct the ensemble, but may not realize all of the behind-the-scenes work that the director must do in order to ensure that any show runs smoothly.
The main job of the music director is to conduct the musical ensemble being used for any particular concert or show.
During rehearsals, the music director conducts the musical -- and sometimes vocal -- ensemble. He is in charge of making sure the musicians are prepared for their performances and for making any changes in the score that he deems fit.
Auditions are coordinated and often led by the musical director. The auditions are used to decide which musicians will be used in the ensemble, and they are used to establish which parts musicians will play within the ensemble.
Music directors can also act as arrangers -- especially when making cuts in the score, transposing parts to better fit a vocalist's range or adding transitions between numbers.
Often, the musical director will be responsible for choosing and rehearsing the choir, alongside the orchestra or band.