Thermally induced dehydrochlorination is a well-established and prominent degradation mode for vinylidene chloride copolymers. During extrusion, other processes may represent significant degradation pathways. Under shear in air, both oxidative chain-scission and cross-linking are prominent processes for both vinylidene chloride/vinyl chloride and vinylidene chloride/methyl acrylate copolymers. Both processes are dependent upon shear rate and temperature. The shear-stress dependency can be modeled by a kinetic expression that incorporates shear stress into the Arrhenius preexponential factor. Vinylidene chloride/methyl acrylate copolymers appear to be somewhat more susceptible to oxidative chain-scission than are comparable vinylidene chloride/vinyl chloride copolymers, presumably because of a rapid oxidative attack at exposed methyl acrylate units. Shear-induced degradation of these materials in air is characterized by early predominant chain-scission with cross-linking assuming a greater importance as a function of time. Degradation under shear in a nonoxidative environment is a much simpler process-oxidative chain-scission is suppressed and cross-linking is very similar to that observed in air.