As the leaders of their orchestras, conductors are responsible for coordinating the efforts of one hundred or more performers into a cohesive and expressive whole. These men and women go well beyond marking tempos and reminding musicians when to enter -- they have a pervasive influence on the subtleties of a given performance. Phrasing, stylistic considerations, ensemble blending, timbre, and emotional nuance are just some of the concepts conductors flesh out during the hours of rehearsal outside the public's view. Moreover, the charisma required to lead an orchestra full of prima donna musicians is immense. The conductor can make or break the success of an orchestra.