Polyester is one of the most important polymers for fibers and composites. Significant developments in nanoparticle-doped polyester composites, polyester recycling, flame-retardant unsaturated polyester resins, and application of polyester for construction and automotive industry are currently carried out. Thus, this book provides leading edge research on improvements of functional properties of polyester, modifications of unsaturated polyester resins, and polyester (especially recycled polyester) usage in construction and in automotive application areas in the form of fiber, resin, and composite. The book also covers the characterization of unique features of polyester found by mechanical, chemical, physical, microstructural, and thermal analyses. This book intends to provide an understanding of the developments of functional polyester production, synthesis, and characterization and support to many academic researchers and graduate students in textile, polymer, composite, chemical science, and research and development managers in recycling and composite applications of polyester in the construction and automotive industry.