The X-ray extended-range technique (XERT) is an advanced high-accuracy technique for X-ray attenuation, X-ray absorption spectroscopy (XAS), X-ray absorption fine structure, X-ray absorption near-edge structure and fluorescence XAS which has been developed and applied at several beamlines around the world. The statistical precision and accuracy of data obtained using XERT, compared with standard experiments using the same beamline and flux, are normally improved by a factor of 10–100. Of course, it takes a longer period of data collection in order to return greater physical and chemical insight. XERT has successfully been applied across the energy range from 5 to 60 keV. It has been applied to elemental materials from silicon (Z = 6) to tin and gold (Z = 79) and it has been applied to K edges and L edges. It has successfully been applied to mono­elemental metal foils, solid compounds, crystals and concentrated (15 mM) and dilute (1.5 mM) solutions, and to systems with from 100%(w/w) to 0.07%(w/w) of the active species in the molecule of interest. XERT has measured attenuation and absorption coefficients from 4 to 340 g cm⁻² with samples of thicknesses from 1 µm to 4 mm and natural logarithm ratios 0.01 < ln(I₀/I) < 9. XERT has been applied to transmission measurements and fluorescence measurements, and to active-species attenuations as low as ln(I₀/I) = 0.001 for solutions. The principles, techniques and technology of XERT should directly carry across to soft X-ray, in vacuo and vacuum ultraviolet energies. Whereas standard XAS may attain a precision or accuracy as low as ∼1–10%, XERT has regularly reached a precision and accuracy of 0.1% or 0.02%, depending upon the material, beamline and energy regime. Simpler approaches have many valid purposes, but the higher accuracy of XERT permits several novel opportunities: (i) investigations of nanostructure and local structure, and not just `fingerprinting', (ii) determination of nano­structure against multiple hypotheses, and not just `confirmation of structure from some other technique', and (iii) ab initio structural determination that is equal to, or in some cases better than, that from X-ray diffraction for local structure (Glover & Chantler, 2007). This accuracy permits the observation of dynamic structure, and the evolution thereof, compared with the anisotropic thermal parameters and ellipsoids obtained from X-ray or neutron diffraction. For many fundamental questions, it is a key tool for future research.