Аннотация:This chapter discusses the resonance elastic and inelastic x-ray scattering processes for the in-situ investigation of electrochemical interfaces. X-ray-in and x-ray-out methods with high-energy and high-brilliance x-rays are some important techniques that can be used for the study of electrochemical interfaces. The most widely used technique is x-ray absorption spectroscopy (XAS). An advantage of the x-ray techniques is that they are highly versatile. They have been powerful in case of both single-crystal electrode interfaces and nano-structured electrochemical interfaces. In addition, they serve as promising tools for the surfaces of nanoparticles. This chapter elaborates on the potential new x-ray applications beyond ordinary XAS. Most techniques are possible only because of third-generation synchrotron x-ray sources. The scattering probability of x-rays at an atom can be enhanced when the photon energy is close to an absorption edge of the atom. This is similar to classical resonance phenomena. The discreteness of electronic energy levels in atoms or molecules is inherently quantum mechanical in nature. A quantum mechanical description of the resonance phenomena has also been reviewed in the chapter.