Charged particles approaching or leaving a solid surfacescatter inelastically on the long-range Coulomb field of real or virtual surfacecollective excitations of the solid. A quantum theory of this scattering process, applicable to the case of “fast” particles, is presented. Two particular examples are discussed: (i) electron spectroscopy of surface plasmons in metals; (ii) observation of surface “plasmons” in transition metals excited by field emitted ions in field ion microscopy.