UCSD's IR astronomy group is building an imaging mid-IR spectrometer for the Keck Telescope. This instrument, the Long-Wavelength Spectrometer (LWS), is built around a 96 X 96 element, Si:As impurity band conduction array built by GenCorp Aerojet Electronics Systems Division. The LWS has low and moderate spectroscopy modes with nominal spectral resolutions of R (equals (lambda) /(Delta) (lambda) ) equals 100 and 1400 respectively, operating in the 10 micrometers (second order) and 20 micrometers (first order) ground- based atmospheric spectral windows. The LWS is also capable of direct imaging from 5 micrometers to 27 micrometers through a selection of 16 filters. For each of the spectroscopic modes and the direct imaging mode, the plate scale is 0.12 arcsec/pixel, which Nyquist samples the telescope's diffraction pattern at 10 micrometers . Because of the large light gathering power of the Keck Telescope and it's small diffraction pattern, the LWS will have unparalleled point source sensitivity, making it the premiere instrument for extragalactic and general faint-source mid-IR spectroscopy.