This book presents investigation results of thermal transformations in thermoresistant polymers: polysulfones, polyester-imides, aliphatic-aromatic polyimides and polyamides, liquid-crystal aromatic co-polyesters, polyphenylquinoxalines at temperatures of materials and articles processing and operation. An important result of investigations is the determination of thermooxidative degradation regularities for aliphatic-aromatic heterochain polymers and description of the degradation mechanism. The applied aspect of this work is the approach to stabilization of thermoresistant polymers and composite materials derived from them using additives and analysis of the mechanism of high-temperature inhibited oxidation. The book presents results which have been obtained through many years of research until recently, mostly obtained by scientists of G.S. Petrov Research Institute of Polymeric Materials (Moscow, Russia) – one of the leading Institutes in this branch - which have not been available in international scientific publications before.