This chapter addresses the structurerheology relationship in compatibilized blends. It focuses on the effects of the compatibilizer on the structural evolution, rather than on the effectiveness of specific compatibilizers or the physical properties of the ultimate compatibilized blends. The blending of immiscible polymers is an economically attractive route to develop new materials that combine the desirable properties of more than one polymer without investing in new chemistry. When small droplets in an uncompatibilized polymer blend are sheared at low capillary number, their size increases because of coalescence. Commercial blends typically consist of high molecular weight polymers that are processed at high temperatures in the molten state. Such components typically exhibit significant elasticity, especially at the high shear rates encountered in processing equipment. Systematic relaxation experiments on concentrated blends, either studied by rheology or by other in situ methods, are scarce in the literature.