A large variety and number of electro-optic (EO) systems have been developed for radar, communications, platform guidance, sensor functions, etc. In considering these applications many technical questions regarding undesirable electromagnetic (EM) effects which may degrade the operation of an EO system are apparent. Information and data related to these effects is presented. These effects include atmospheric scattering, dust and chemical films on apertures, and edge scattering effects which are expected to modify the theoretical diffraction pattern. Emission spectrum characteristics in terms of sideband, spurious, and harmonic energy as well as RF emissions are discussed. Out-of-band response of EO detectors and filters, spurious responses due to non-linearities, detector desensitization, and RF frequency degradation effects on EO receivers are considered. The analogy of EO systems to RF system problems is stressed to illustrate the potential loss in performance due to these undesirable effects.