Experimental results obtained during the past 50 years in studying the compatibility between the components in rubber-containing blends and solutions under static conditions and in the presence of mechanical field have been surveyed and analyzed. Phase diagrams of polymer-polymer and polymer-polymer-solvent systems are presented. Causes of phase separation of the systems are considered. The corresponding phase diagrams are analyzed with respect to the chemical macromolecular structure of polymer components. Changes in phase separation temperatures of the polymer systems under shear deformation are discussed; inversion in the effect of the mechanical field on the solubility of the constituent components is described; at low strain rates, solubility appears to be improved, whereas at high strain rates, solubility decreases.