The book focused on the practical aspects of reactive compatibilization-cum-impact modification of complex systems containing both virgin polymers and/or their mixed plastic waste. This issue is critical for waste management as the mechanical recycling is the most viable method, it demands sorting of plastic waste for homogeneous streams- a costly process. Possibility of avoiding this stage by means of reactive compatibilization would make reprocessing much simpler and cheaper in parallel with providing high quality of the end products based on recyclates. The findings on a combined method of compatibilization and impact modification obtained by the authors for virgin polymers like polyolefins (LDPE and PP) and polyamide 6 (PA6) have been also verified for the blends of virgin/recycled polymers. LDPE and PP have been melt functionalized with three polar monomers and further used as reactive compatibilizers, while ethylene-propylene-diene (EPDM) termonomer has been used as an impact modifier. Complex investigations and characterization of advanced multicomponent polymeric systems carried out in this book provided several innovative results, both with scientific and practical value.