The ECL (Ecole Centrale de Lyon) surface force apparatus (SFA) has been developed and refined over the last two decades. This paper reviews a number of applications of the SFA that are of interest to the tribologist. In order to predict and improve contact performance, the tribologist needs to understand and quantify the basic properties of the lubricant and the solid bodies it is separating. Previously, these important properties were the material bulk properties, or at least these properties were sufficient. This situation is no longer true, and the material properties of the solids and the lubricant are required on a scale which is small or comparable with the film thickness. Nowadays, that means a scale small or comparable with 10(-7)-10(-8) mi It is in this domain that the SFA can provide information on mechanical properties of very thin lubricant films, and on the properties of the solid material close to its surface.