A polymer is a large molecule (macromolecule) composed of repeating structural units typically connected by covalent chemical bonds. While polymer in popular usage suggests plastic, the term actually refers to a large class of natural and synthetic materials with a variety of properties. Due to the extraordinary range of properties accessible in polymeric materials, they have come to play an essential and ubiquitous role in everyday life -- from plastics and elastomers on the one hand to natural biopolymers such as DNA and proteins that are essential for life on the other. This book examines the role polymers play as natural nanocomposites.