NIST X-ray Photoelectron Spectroscopy (XPS) Database gives easy access to the energies of many photoelectron and Auger-electron spectral lines. Resulting from a critical evaluation of the published literature, the database contains over 22,000 line positions, chemical shifts, doublet splittings, and energy separations of photoelectron and Auger-electron lines. A highly interactive program allows the user to search by element, line type, line energy, and many other variables. Users can easily identify unknown measured lines by matching to previous measurements. Version 4.1 which contains an additional 4368 data records for a total of over 33,000 data records. Version 4.1 also contains new reference photoelectron binding energies, reference Auger-electron kinetic energies, and reference Auger parameters for many elemental solids from recent analyses of Handbook data. Wagner plots are now available for 61 elements.