Tribology is an engineering field that deals with friction, wear, and lubrication. It plays a crucial role in improving the energy efficiency, durability, and reliability of mechanical systems. While friction and wear phenomena are observed as macroscopic events, their fundamental mechanisms are largely governed by atomic and molecular behaviors at the frictional interfaces. Therefore, surface analysis techniques aimed at elucidating these mechanisms are key to advancing tribology technologies. However, frictional interfaces exist in a dynamic, non-equilibrium state, exposed to high temperatures, high pressures, and high shear fields. This has made it challenging to obtain sufficient information using conventional surface analysis methods. In recent years, the application of in situ or operando analysis techniques, which allow for real-time observation of the states at frictional interfaces, has gradually shed light on friction and wear phenomena that were previously considered black boxes. This article introduces in situ analysis techniques for investigating frictional surfaces.