This chapter deals with the development of the phase morphology in polymer blends with an emphasis on micro- and nanophase morphologies. It focuses on the relationships between phase morphology and ultimate mechanical properties. Polymer blending has been identified as the most versatile and economical method to produce new multiphase polymeric materials that are able to satisfy the complex demands for performance. The morphology formation during melt-mixing of immiscible polymers involves processes such as liquid drops stretching into threads, breakup of the threads into smaller droplets, and coalescence of the droplets into larger ones. A fine dispersion in fluoroelastomer/semicrystalline perfluoropolymer nanoblends has been obtained with an innovative mixing technology based on microemulsion polymerization. Recycling of polymer blends and multilayered structures is still a major challenge. The recycling of automobile parts will probably be an active area in which blending know-how will be a key to success.