MIRSI (Mid-InfraRed Spectrometer and Imager) is a mid-infrared camera system recently completed at Boston University that has both spectroscopic and imaging capabilities. MIRSI is uniquely suited for studies of young stellar objects and star formation, planetary and protoplanetary nebulae, starburst galaxies, and solar system objects such as planets, asteroids, and comets. The camera utilizes a 320 x 240 Si:As Impurity Band Conduction (IBC) array developed for ground-based astronomy by Raytheon/SBRC. For observations at the Infrared Telescope Facility (IRTF), MIRSI offers a large field of view (1.6 arcmin x 1.2 arcmin) with a pixel scale of 0.3 arcsec, diffraction-limited spatial resolution, complete spectral coverage over the 8-14 μm and 17-26 μm atmospheric windows for both imaging (discrete filters and circular variable filter) and spectroscopy (10 and 20 μm grisms), and high sensitivity (expected one-sigma point source sensitivities of 5 and 20 mJy at 10 and 20 μm, respectively, for on-source integration time of 30 seconds). MIRSI successfully achieved first light at the Mt. Lemmon Observing Facility (MLOF) in December 2001, and will have its first observing run at the IRTF in November 2002. We present details of the system hardware and software and results from first light observations.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.