We present a description of the mid-IR camera system (MIRCAM) currently under development at the University of California, Irvine. MIRCAM is a portable imaging system, specifically designed for diffraction-limited, broadband imaging in the 4.7 micrometers (M band), 10 micrometers (N band), and 20 micrometers (Q band) atmospheric windows. MIRCAM is designed for operation with the new generation of high-background 256 by 256 Si:As IBC arrays currently under development by both Rockwell International and Hughes Aircraft. However, initial operation will proceed with a 128 by 128 Si:As IBC array manufactured by Rockwell International. We have also designed a state-of-the-art control and data-acquisition system that is capable of reading out the 256 by 256 array at a rate of 500 frames per second, or 2000 frames per second for the 128 by 128 array. The fully-reflective optics are designed for Nyquist-sampling at the telescope diffraction limit, and exhibit spot sizes that are considerably smaller than the pixel size over the entire 256 by 256 array. Four interchangeable optical configurations permit use of MIRCAM on the Lick 1-m, IRTF 3-m, UKIRT 4-m, and Keck 10-m telescopes.