The application of synchrotron X-ray techniques has led to major advances in our understanding of the electrode–electrolyte interface and electrode processes. X-ray techniques such as glancing incidence X-ray scattering and X-ray reflectivity have contributed greatly to our understanding of the electrode–electrolyte interface. Hard X-rays (with energies of ∼5–15 keV) have a large penetration depth in aqueous solution (∼1 mm), which permits in situ measurements. X-ray wavelengths are comparable to atomic dimensions, and hence, X-ray scattering techniques probe structure at an atomic scale. However, the weak interaction of X-rays yields small signals. In a typical in situ experiment a flat electrode surface contains ∼1014 atoms, so the signal is small. The problem is exacerbated by scattering from the ∼1020 atoms in the electrolyte. However, these difficulties have been overcome with the use of the intense radiation from synchrotron sources. X-ray absorption spectroscopy is another very powerful synchrotron X-ray probe. It yields both chemical information and short-range structural information. This issue contains a collection of 20 papers devoted to the application of synchrotron X-ray scattering and spectroscopy in electrochemistry. Almost all of these papers involve in situ studies. The papers illustrate the many aspects of electrochemistry that can be investigated by synchrotron X-ray techniques. Because of the diversity of the areas covered, the papers are arranged as follows:•The Electrode–Electrolyte Interface.•Corrosion.•Lithium Battery Materials.•Electrocatalysts for Fuel Cells and Metal–Air Batteries. The Electrode–Electrolyte Interface. Corrosion. Lithium Battery Materials. Electrocatalysts for Fuel Cells and Metal–Air Batteries. All are invited papers. The papers were reviewed and all the accepted papers underwent either minor or major revisions. I would like to express my gratitude to all the authors of this Special Issue and I am indebted to the referees.