The Compact Scanning Submillimeter-wave Imaging Radiometer (CoSSIR) is an airborne, 12-channel, (183 - 874 GHz) total power imaging radiometer that was mainly developed for the measurements of ice clouds. But it can be used for estimation of water vapor profiles and snowfall rates. When first completed and flown in the CRYSTAL-FACE field campaign during July 2002, the system had 15 channels at different frequencies from those listed below. All the receivers and radiometer electronics are housed in a small cylindrical scan head (21.5 cm in diameter and 28 cm in length) that is rotated by a two-axis gimbaled mechanism capable of generating a wide variety of scan profiles. Two calibration targets, one maintained at ambient (cold) temperature and another heated to a hot temperature of about 328 K, are closely coupled to the scan head and rotate with it about the azimuth axis. Radiometric signals from each channel are sampled at 0.01 sec intervals. These signals and housekeeping data are fed to the main computer in an external electronics box.