X-ray absorption spectroscopy (XAS) uses standards in many contexts, especially in (i) reference metal foil determinations and calibrations of the monochromator energy and the energy on the sample, (ii) definitions or measurements of the edge energy for the extraction of χ, (iii) measurements of chemical shifts of the edge and pre-edge features, whether for fingerprinting or for principal component analysis, and (iv) measurements of a normalizable absorption coefficient. This chapter summarizes common approaches and some recommendations for XAS.