This book gives a thorough overview on recent developments in lubricant rheology, elastohydrodynamic lubrication and the effects of surface roughness and particulate contamination in the lubricant on the overall behaviour of a heavily loaded lubricated contact. One of the aims of the book is to make clear to the reader that a Newtonian model for the lubricant behaviour does not have enough degrees of freedom to be able to describe the friction - traction behaviour of heavily loaded lubricated contacts or the oil film build-up and collapse under surface asperities for rough surfaces. The book contains quite a lot of experimental data of lubricants at high pressures, both solidification pressures, compressibilities and shear strength increase coefficients, which make it possible to estimate the friction and power loss in heavily loaded lubricated contacts for different pressures, temperatures, sliding speeds, and lubricant types. This is the first time that data of this type has been included in a textbook and it is hoped that the questions highlighted will serve to initiate and guide future research in this field.