Publisher Summary This chapter describes the theory of mixed lubrication and discusses experimental considerations, pitting in rolling/sliding contacts, lubricant–metal interaction effects in fatigue, wear in rolling/sliding contacts, and modeling of contact in mixed lubrication. Asperity contact through the films is of practical importance. Improved mixed lubrication is a desirable goal to be achieved in practice. Wear occurs due to relative sliding among surfaces. Pitting life is extensively studied because of its effect on failure. The wear problems in these contacts are less widely studied. Once the pitting problem is overcome, the component life will be determined on the basis of allowable wear in the system. In mixed lubrication, the wear modeling can be approached in terms of the extent of asperity contact through the films. The influence of chemical additives is variable. Most of the chemical additives tried have a significant beneficial effect on wear in normal boundary lubrication. These include conformal and concentrated contacts.