In the training of mechanical engineers and manufacturing technicians, lubricants are only addressed to the extent that they exist and have an impact on tribological systems. A deeper exploration does not take place, especially considering the complex chemical relationships involved. This book sheds light on the dark side of tribology and explains the function of the interfacial substance. Existing literature is critically evaluated, and models are presented as a supplement. The monograph helps readers gain a better understanding of the interactions on metal surfaces and in the boundary layer of components.