Polymeric composites are indeed a significant and indispensable topic in scientific research today. These materials play a crucial role in various industries due to their unique combination of properties that often cannot be achieved by using a single material. This chapter briefly covers the fundamentals and major applications of polymer composites nanocomposites and fiber-reinforced polymers (FRP) composites. Additionally, the authors briefly discussed the significance of the durability study of the polymer and FRP composites. © 2024 Elsevier Ltd. All rights reserved.