 Surface sensitivity is achieved by detecting photoelectrons with kinetic energies of about 10-1000 eV, which have corresponding inelastic mean free paths of only a few nanometers.This technique has been extended to operate at near-ambient pressures (ambient pressure XPS, AP-XPS) to probe more realistic gas-solid and liquid-solid interfaces.Performing XPS with hard X-rays at synchrotron light sources yields photoelectrons with kinetic energies of several keV (hard X-ray photoelectron spectroscopy, HAXPES), enabling access to chemical information from buried interfaces.