A pit orchestra is a type of orchestra that accompanies performers in musicals, operas, ballets and other shows involving music. The terms was also used for orchestras accompanying silent movies when more than a piano was used. In performances of operas and ballets, the pit orchestra is typically similar in size to a symphony orchestra, though it may contain smaller string and brass sections, depending upon the piece. Such orchestras may vary in size from approximately 30 musicians (early Baroque and Classical opera) to as many as 90–100 musicians (Wagnerian opera). However, because of financial, space, and volume concerns, the musical theatre pit orchestra in the 2000s is considerably smaller (at most 20–30 musicians, including not more than ten string players).
Typically, pit orchestras play in a lowered area in front of the stage called an orchestra pit. Inside the pit, the conductor stands facing towards the stage with his or her back towards the audience to coordinate the music with the vocals and actions of the singers, dancers and actors, while the orchestra sits facing the conductor. The conductor may also sit at one or more keyboards and conduct as well as play, which often means the use of more head and facial gestures rather than hand gestures. This is often the case when a show only requires a small orchestra, or on national tours, where the instrumentation is often reduced from the original arrangement and one or two keyboard players substitute for several instruments. In some cases, theatres do not have a pit; in this case, the pit orchestra may play in a room near the stage, watching the conductor's gestures using a video monitor.
Music parts for pit orchestra woodwind players in musical theatre are normally divided into "reed books". Orchestration varies with each show based on the type of music that will be performed, such as jazz, classical, or blues. For example, a Reed 1 Book may contain music for piccolo, flute, Eb alto saxophone, Bb clarinet, and/or oboe. A musician handed a reed book would be expected to play each part. Because the musician plays so many different instruments, he or she is referred to as a "doubler" (even though the Reed Books may have up to eight instruments each).