The term tribology is scarcely twenty-five years old and yet there can be few university or college courses in mechanical engineering which do not now include material under this heading. Of course, the problem of producing bearings, slides, seals, and other tribological systems to give smooth machine running and long component lives is one which has faced practitioners for generations, and consideration of their design has always played a part in the education of mechanical engineers. What has become increasingly obvious in recent years is the inherently interdisciplinary nature of the tribologist's task; as well as involving practising and academic engineers, advances in the subject have drawn upon the ingenuity and expertise of physicists, chemists, metallurgists, and material scientists. Consequently, although envisaged principally for use by final year undergraduates and post-graduate students in mechanical engineering, I hope that this volume may be of interest to students and specialists in these other related areas. Tribology is still very much an area of active research and the published literature in the fields of lubrication, friction and wear–already dauntingly voluminous–continues to grow at an alarming rate. I have made no attempt to produce a research monograph but rather to provide a framework of fundamental analytical tools which can be used in a wide variety of different physical situations. Each chapter is concluded with a short list of suggestions for further reading which provide access to the more specialised literature.