In this book, an internationally known team of researchers publish state-of-the-art results that detail the application of synthetic, petroleum-based polymers in the form of carbon fibers, carbon nanotubes and fibers, and micro- and nanofibrils as reinforcements for polymer composites. These organic materials are distinct from polymer composites with mineral reinforcement due to specific mechanical properties that allow the manufacture of lightweight products, of particular importance in aircrafts and transportation vehicles. With over fifty contributors and twenty-three comprehensive chapters, this book provides another approach for the replacement of glass- and other inorganic fibers as reinforcement for polymer composites. It is a must-have for polymer blend, natural polymer, and composite specialists, as well as for automobile manufacturers, waste mangers, and researchers and students in these fields. Major Topics Covered: Introduction to Synthetic Polymer-Polymer Composites Polymer-Polymer Composites with Premade Fibrous Reinforcements In situ Nano- and Microfibrillar Polymer-Polymer Composites Single Polymer Composites