We present a compilation of data for all 258 gamma-ray flares detected above 300 keV by the Gamma Ray Spectrometer (GRS) aboard the Solar Maximum Mission satellite. This gamma-ray flare sample was collected during the period from 1980 February to 1989 November; covering the latter half of the 21st solar sunspot cycle and the onset of the 22d solar sunspot cycle. We describe the SMM/GRS instrument, its in-orbit operation, and the principal data reduction methods used to derive the gamma-ray flare properties. Utilizing measurements for 185 flares that were sufficiently intense to allow the derivation of gamma-ray spectra, we present an atlas of time profiles and gamma-ray spectra. The flare parameters derived from the gamma-ray spectra include bremsstrahlung fluence and best-fit power-law parameters, narrow nuclear line fluence, positron annihilation line fluence, neutron capture line fluence, and an indication of whether or not emissions greater than 10 MeV were present. Since a uniform methodology was adopted for deriving the parameters, this atlas should be very useful for future statistical and correlative studies of solar flares.