The Cosmic Ray Isotope Spectrometer (CRIS) on the Advanced Composition Explorer (ACE) spacecraft is intended to be a major step in ascertaining the isotopic composition of the cosmic rays and hence a major step in determining their origin. The GCRs consist, by number, primarily of hydrogen nuclei (~92%) and He nuclei (~7%). The heavier nuclei (1%) provide most of the information about cosmic-ray origin through their elemental and isotopic composition. The intensities of these heavy cosmic rays are very low and progress in the past has been impeded by limited particle collection power, particularly regarding individual isotopes. CRIS is designed to have far greater collection power (~250 cm?-sr) than previous satellite instruments (< 10 cm?-sr) while still maintaining excellent isotopic resolution up through Z=30 (Zinc) and beyond.