This Special Issue explores significant research on fiber-reinforced thermoplastic composites, including advancements in material development, process optimization, sustainability, and multimodal characterization techniques. Featured topics include low-density, high-performance composite foams, flame-retardant panels, and eco-friendly bio-composites using flax and cashew nut shells. This issue also examines optimizing processing methods like hot runner systems and enhancing recycled-fiber composites. These studies offer valuable insights into the evolving landscape of composite materials.