This book on polymer tribology explores the gradual replacement of metal components by polymer-based materials (PBM's) that is taking place in automotive, aviation, aerospace, and other industries. The positive results include lower weights of components and entire structures as well as significant energy savings (more miles per gallon). Metals cannot be scratched easily, while polymeric surfaces have, in general, low scratch and wear resistance. Teflon is widely used because of its low friction but the residual scratch depth in Teflon is three times larger than in polyproplene, not even comparing with that in metals. Progress in tribology of PMB's has hampered by how little we understand it.