The problem/need addressed in this book is the recognition of the various ways that wear erosion and friction manifest themselves in machines, devices, and engineering and science in general. It is about what tribology looks like in the field. As is the case in the health care industry, treating an illness starts with a diagnosis of the malady. This is a critical first step in addressing any health problem. It is also like this in tribology. Solids do not just wear or erode; they do so in many different ways-different mechanisms prevail and different treatments are necessary. The common factor in wear and erosion is progressive loss of material from solid surfaces, but how that occurs is the key to minimizing losses and solving problems that arise for these progressive material losses.