TERPSICHORE: A Three-Dimensional Ideal Magnetohydrodynamic Stability Program. The 3D ideal magnetohydrodynamic (MHD) stability code TERPSICHORE has been designed to take advantage of vector and microtasking capabilities of the latest generation CRAY computers. To keep the number of operations small most efficient algorithms have been applied in each computational step. The program investigates the stability properties of fusion reactor relevant plasma configurations confined by magnetic fields. For a typical 3D HELIAS configuration that has been considered we obtain an overall performance of 1.7 Gflops on an eight processor CRAY-YMP machine.