Lubrication is a process in which a lubricant is placed between rubbing surfaces to control friction and reduce wear. This article outlines the nature of the frictional force, the wear process, the role of surface characteristics, and the mechanisms of lubrication. The manufacture and classification of lubricating oil base stocks, including refined petroleum stocks, chemical base stocks, stocks synthesized from other chemicals, and vegetable oils, are covered. The composition and function of lube oil additives are described for enhancing oxidation stability, corrosion resistance, wear reduction, friction modifying, viscosity–temperature characteristics, and other important performance characteristics. The performance characteristics of lubricating oils for selected applications are discussed, including automotive engine oils, diesel engine oils, automatic transmission fluids, automotive gear oils, jet engine lubes, and industrial turbine oils. Metalworking fluids, lubricating grease, solid-film lubricants, and lubrication in extreme environments are covered, as are the lubricants market and environmental and health concerns. Keywords: friction; lubricants; lubrication; viscosity; wear