This article presents a general overview of outdoor weather aging factors, their effects on plastic materials, and the accelerated test methods that can be used to estimate the reaction of a plastic component during actual use. Weather and radiation factors that contribute to degradation in plastics include temperature variations, moisture, sunlight, oxidation, microbiologic attack, and other environmental elements. The article also describes the tests used to predict the behavior of a plastic material to outdoor exposure, discussing the use of xenon arc lamp for the weatherometer and fadeometer and the use of fluorescent sunlamp in test devices.