The Gamma-Ray Imaging Spectrometer (GRIS) was a gamma-ray spectrometer instrument on a balloon-borne airborne observatory. It used germanium detectors to achieve high resolution spectroscopy. GRIS was operated from 1988 to 1995 by NASA's Goddard Space Flight Center which called it "arguably one of the most successful gamma-ray balloon programs in history". GRIS followed earlier gamma ray spectroscopy work by Bell Labs/Sandia National Laboratories and co-investigators Marvin Leventhal and Bonnard Teegarden including the LEGS spectrometer. GRIS was selected for a balloon program after the removal of a high-resolution gamma-ray spectrometer from the payload of what would become the Compton Gamma Ray Observatory.