Multicomponent polymer blends, for improving both process and product related properties, often require the optimization of interfaces/ interphases. This is particularly true in the case of blends based on recycled polymers. Besides a review of existing approaches, two examples are presented in more detail. The former is related to the toughening of recycled PET (poly(ethylene terephthalate)) by reactive ethylene-ethyl acrylate_glycidyl methacrylate elastomers. The effect of catalysts of the reaction between elastomer epoxide functions and PET carboxyl and hydroxyl end-groups and of impurities introduced during recycling has been assessed. Variations of rheological behavior, morphology of chips and molded parts, and mechanical properties have been examined and related to interfacial chemistry. The formulation with glass fibers has also been experimented with, gaining interesting information on the compromise between resilience and rigidity. The second example is related to the so called 'light fraction' of recycled polymers, concerning mainly polyethylene (PE) and polypropylene (PP). Mixing has been performed in various relative amounts, as such and in the presence of initiators inducing both bulk and interfacial radical reactions. Effects on rheology, morphology and mechanical properties have been assessed, observing that the initiation of reactions is an important tool for improving the interfacial behavior.