The stability of polymeric substances in oxidizing atmospheres is almost always quite different from that observed in nonoxidizing media. The methods and techniques applicable to studies of the chemical changes taking place in a number of complex condensation polymers have been examined in detail in an effort to draw from the resultant data fundamental information regarding the mechanisms of thermooxidative degradation processes. In general terms, it has been of interest to examine condensation polymers at various stages of curing in both oxidizing and inert atmospheres in order to elucidate the chemical transformations that contribute to the over-all stability of these polymers. The use of structural modifications in specific polymer systems together with model-compound studies, solid-phase monitoring of functional-group changes, and gaseous-product analysis are exemplified as they pertain to an investigation of detailed degradation reactions. The results of these investigations and the mechanistic conclusions that can be drawn offer a ready source of information pertaining to the effects of processing upon the thermal life of particular polymers in oxygen-containing atmospheres and, in addition, they offer data concerning the effect of specific linkages within the polymer unit upon the over-all stability of the polymer. Such information is extremely valuable from a viewpoint of new polymer synthesis and stabilization methods for existing complex polymer systems.