AbstractIn this paper certain aspects concerning the influence of rheological parameters on the morphology of immiscible polymer blends are considered. The author reviews his own work with reference to other key studies carried out in the field. The influence of the viscosity ratio on morphology for compatibilized and non‐compatibilized systems are treated, as well as the influence of shear stress. The role of viscosity and viscosity ratio in controlling co‐continuous and complex composite droplet morphologies are also discussed.