The artificially intelligent computer performer is a software program that enables a computer to accompany, in real-time, live performers. The computer is, in effect, a participating member of a musical ensemble. It interacts with the musicians by listening to them and it makes musical decisions based on what it hears and what it knows about music. The computer performer uses parallel processing to speed up its response time. The implementation of the system is discussed, the tracking algorithm and the subsequent computer response are described, and then ongoing and future work are outlined. Musical considerations which have influenced the development of the system are also discussed.