Substantial improvements in the thermal imaging state-of-the-art are occurring in forward-looking infrared (FLIR) system technology. These far infrared imaging systems have achieved broadcast television standards for frame rate, resolution, and signal-to-noise ratio, and are moving toward the standardization and volume production necessary for wider dissemination of the technology. Current techniques permit a single-detector system to approach within a factor of two the theoretical limit of thermal sensitivity using a photon detector. FLIR systems now use mechanical scanners and the mini-mum number of detectors necessary to achieve the needed performance, but performance requirements are increasing, and future systems may use mosaics of self scanned detec-tors. Then problems of element-to-element nonuniformities and of background substraction must be solved.