Polymer nanocomposites are polymer-based composites in which the reinforcement is in nano size. The nano size provides tremendous surface area for the unit weight of the material, and thus the matrix-reinforcement contact area increases tremendously. The properties of a composite depend on the amount of this contact area. The larger the contact area, the greater the property improvement. Thus, the knowledge of polymer nanocomposites is important for their proper use in applications. This book provides such knowledge. It discusses all the aspects of polymer nanocomposites, namely, their synthesis, characterization, properties, and applications. It covers general as well as specific polymer nanocomposites, throws light on recent research and development, and describes current and prospective applications.