Energy- and intensity-tunable monochromatic X-ray sources enable new developments in X-ray metrology. The fundamental parameters characterizing photon-matter interactions can be determined with relative standard uncertainties around 1–2%. The characteristics of the SOLEX laboratory source and of the SOLEIL synchrotron radiation source are discussed. The procedures for measuring mass attenuation coefficients and fluorescence yields are detailed; examples are presented for copper, cadmium and germanium. These new sources with associated instrumentation will allow developing improved techniques for reference-free quantification by X-ray fluorescence.