Polymer nanocomposites have attracted the research community in the recent years owing to its unique physical and chemical properties. The polymer nanocomposites combine the physical and chemical properties of polymers with the properties of nanoparticles in order to provide combined physical and chemical properties. Commonly used synthetic reinforcing materials, like carbon, silica, nanoclays such as MMT, and metal hydrides, and their impact on the modulus, strength, and fatigue resistance of the polymers, are discussed. They are also lightweight, are strong, and have excellent thermal and electrical properties, making them an ideal material for many applications. Due to its multitudinous applications which require enhanced properties, like mechanical strength, electrical conductivity, thermal conductivity, etc., which can be achieved due to the incorporation of nanofillers into the polymer matrix, various synthesis routes to fabricate such structures and studies on polymer nanocomposite properties are discussed in detail. A detailed discussion of the applications of polymer nanocomposites is provided, which allows the development of novel materials. © 2025 selection and editorial matter, Atul K. Maurya, Gaurav Manik, and Sushanta K. Sethi; individual chapters, the contributors.