A Mueller matrix imaging polarimeter has been developed and demonstrated for characterizing the polarization properties of optical coatings in place in optical systems. This Mueller matrix imaging polarimeter is a form of ellipsometer which measures the polarization characteristics of ray paths through systems in image form. It is a highly versatile instrument capable of making a variety of polarimetric measurements on optical samples or entire optical systems. Two data sets will be presented. The first shows the polarization behavior for example lenses which display the typical Maltese cross variation. The second shows images of polarizing beam splitter behavior as a function of angle of incidence, clearly showing how the plane of polarization as determined by the s- and p-planes rotates for light incident out of the normal plane.