The detailed structure associated with X-ray absorption when an X-ray knocks a core electron out of a solid and the electron then interacts with neighbouring atoms. This structure arises because the wave nature of the ejected electron means that internal diffraction and interference can occur when it backscatters from neighbouring atoms. XAFS has been used very extensively in the analysis of materials because the energy of the X-ray absorption required to eject an electron is specific to each element. XAFS can be applied both to crystals and to disordered solids. A suitable source of X-rays for XAFS is synchrotron radiation.

In applications to condensed matter it is customary to divide the XAFS spectrum into three parts. (1) The edge region is several electron volts around the absorption edge. (2) The X-Ray Absorption Near Edge Structure (XANES), sometimes called Near Edge X-Ray Absorption Structure (NEXAFS), extends beyond the edge region by about 50 to 100 electron volts and is associated with multiple scattering from clusters of atoms surrounding the atom that an incoming X-ray interacts with. (3) The Extended X-Ray Absorption Fine Structure (EXAFS) is an oscillating structure that goes to several hundreds of electron volts beyond the absorption edge and is associated with single scattering of the photoelectron by atoms very near to the atom that an incoming X-ray interacts with.