Qualitative and quantitative analyses of the effect of unwanted stray radiation in optical systems are discussed. The basic power transfer equation is written as the product of three factors: the surface BRDF, the projected solid angle, and the power on the source objects. The minimization of any one of these factors along the most significant paths of scatter will reduce unwanted radiation reaching the image. BRDF measurements and their use in selecting suitable coatings are emphasized, along with the effect of altering the baffle configurations, edge scatter, and tolerancing requirements. Optical design aspects, such as stops, field stops, Lyot stops, and obscurations, are discussed in suppressing stray radiation for various systems. The performance and testing of scaled models is related to the expected system performance. The major software tools, GUERAP and APART stray radiation analysis programs, are discussed. The approach presented is to develop qualitative concepts that can be easily grasped by the optical and mechanical designers. The approach should help stimulate stray radiation rejection ideas that can be incorporated during initial design evaluations.