In this study, the Degradation and Miscibility of raw, uncured Nitrile Rubbers, (NBR & HNBR) has been investigated. The ACN (Acrylonitrile Content), Mooney Viscosity and % Hydrogenation are the primary criteria defining each specific brand of these rubbers. Degradation behavior as a function of these parameters was studied. The objective was to assess whether thermomechanical degradation of these rubbers is occurring during the "conditioning" process and if so, to characterize its nature and sort means to prevent it. It was found that thermomechanical treatment does affect these rubbers and that degradation is a combination of chain scission and cross-linking. Molecular parameters were found to effect selection of dominating degradation mechanism. Molecular weight measurements were carried out using light scattering technique. The rheological and light scattering results of the conditioned samples with and without antioxidants were compared to the properties of as received samples. Results were supported by variations in M w (weight-average molecular weight) by light scattering. FTIR was applied as an additional complementary Investigation technique to shed some light on the different functionalities generated during the "conditioning" process. The miscibility study of the two rubbers was performed using a variety of techniques such as rheology, DSC, SEM, Mechanical testing, and Molecular Dynamics. The different techniques agreed in suggesting that the structurally similar HNBR and NBR are mechanically compatible. Molecular Simulation studies showed that these rubbers are not only mechanically but thermodynamically compatible, however due to the nature of these materials segmental miscibility is hard to achieve by conventional methods.