Hydrodynamic lubrication plays an important role in mechanical engineering, although not very many books have been published on the subject. This book was written with graduate students, researchers and designers in view. The first four chapters are preparations for the following five chapters, where several most important subjects in hydrodynamic lubrication are discussed in detail, based on the author's own researches. Examples are oil whip (stability of rotating shafts), foil bearings in connection with magnetic tape storages, squeeze film between rigid surfaces and visco-elastic surfaces, theoretical and experimental analyses of temperature rise in bearings, those of turbulent lubricating film using the k-epsilon model.