Techniques using polarized infrared energy have a potential for developing passive sensors that detect man-made objects in complex natural backgrounds. This detection has the potential of improving the performance of various military systems. This paper addresses the physics of the polarization process, describes the characteristics of targets and backgrounds, and shows how one can compute the polarization seen by a detector. Most natural backgrounds appear to be unpolarized. However, the performance of polarized detection techniques will depend on the degree of polarization clutter encountered; a measurement program is needed to determine the extent of this background polarization clutter.