Data for the energy loss function (ELF) of selected materials compiled from various publications. The imaginary part of the inverse of the dielectric function, Im{−1/ε(k,hω)}, denoted the energy loss function (ELF), is the leading function that describes the material response to account for energy losses of swift electrons in matter. For this reason, it is a practical advantage to express the dielectric function in the form of a parametrized ELF, instead of the dielectric function itself, as input for the calculation of inelastic scattering cross sections. Here the ELF is expressed as a sum of Drude-Lindhard type oscillators (see e.g. Yubero F, Sanz JM, Ramskov B, Tougaard S. Model for quantitative analysis of reflection-electron-energy-loss spectra: Angular dependence. Phys Rev B. 1996;53:9719-9727) The ELF data describe the dielectric properties of materials. It may be applied to calculate energy loss processes of fast electrons moving in a material as well as in geometries met in REELS, XPS and AES where the effect of the surface and a static core hole are included (see e.g. QUEELS-software that can be downloaded at: doi: 10.5281/zenodo.6022426) The data structure is: For each material, a reference to the data for each material is given After a line with @ , the ELF data follows in lines with the following meaning 1. Excitation parameters ac, bc to model core excitations (see Penn, J. Elec. Spectr., 9(1976)29). When ac = 0.001 and bc = -2: no data was available. 2. Energy gap (eV) 3. Refractive Index in the next lines, are the parameters for the oscillators: one line for each oscillator 4. energy position (eV), intensity (eV^2), width (eV), alpha 5. 6. . . Examples of data files that can be directly read by QUEELS for Au and Si are seen in the files ELF_Au.txt and ELF_Si.txt respectively.