The AT-cut quartz crystal shear wave sensor was applied to the study of boundary layer lubrication. The oscillating quartz crystal generates shear waves at its surfaces which propagate into acoustic loads in contact with the surfaces. Measurement of the electrical properties of the sensor allows the viscoelastic properties of the load to be derived. These shear waves are typically absorbed within 2-3 μm of the surface making the quartz crystal an ideal instrument for the study of interfacial phenomena. An instrument was developed which allowed the friction force between the electrode surfaces of the quartz crystal and a matched acoustic load to be measured simultaneously with the viscoelastic properties of a lubricant layer between the surfaces. It was hoped that this instrument would fill the gap between the study of the friction of macroscopic engineering surfaces and the study of atomically perfect surfaces on the nanoscale. Although the sensor proved unable to detect viscoelastic changes in a boundary lubricant layer it was possible to detect the formation of the layer and effects associated with it. The formation of thiol layers from solution and also by sliding of the dry sensor over a thiol multilayer were readily detected. The break-up of confined thin liquid layers was investigated. The response of the sensor to a macroscopic point contact was also studied.