Two typical polymers, polystyrene and polyvinylidene chloride react quite differently to light. The light stability of these two polymers is compared and contrasted. With polystyrene, aging represents the photochemically catalyzed condition of oxygen to unsaturated groups. With polyvinylidene chloride, aging seems to be the photochemically catalyzed loss of hydrogen chloride with subsequent formation of conjugated double bond systems, which may then absorb oxygen. In both polymers the colored reaction forms preferentially at the surface, thus protecting the interior of the specimen from further degradation by light. Polystyrene is stabilized by strong organic amines, whereas polyvinylidene chloride requires an extremely mild acceptor. -- AATA