The lecture includes analysis of principle types of polymer degradation from the viewpoint of their mechanisms and kinetics - i.e. thermal degradation in inert media, termooxidative and photooxidative degradations, biodegradation and chemical degradation. It deals with mechanisms and kinetic aspects of inhibited oxidations, individual types of antioxidants, light stabilizers as well as with mechanisms of their action, mechanism of polymers burning and modes of flame retardation. From other classes of additives, there are described softeners, lubricants, antistatics, foaming agents, colours and pigments, fillers, reinforcements etc. Strategy of formulating complex additivation systems, environmental aspects, recycling and waste liquidation are also discussed.