In this technique, X-rays are made to impinge on the sample surface causing photoelectrons (see XPS) and Auger electrons (see AES) to be emitted from the sample surface.

When a photoelectron is emitted from an atom, a core hole remains, and the atom may emit an Auger electron when the core hole is filled by another electron falling into the core hole. This results in the emission of both a photoelectron and an Auger electron simultaneously. By the detection of both photoelectron and Auger electron from the same process, much can be learned about decay and emission processes over and above what XPS and AES reveal.