This lecture covers the fundamentals and applications of X-ray Photoelectron Spectroscopy (XPS), focusing on electron spectroscopy, energy diagrams, photoemission in the condensed phase, Auger recombination lines, background effects, spin-orbit coupling, multiplet splitting, energy loss lines, shake-up satellites, sample charging, depth profiling, surface contamination, and sputtering techniques. It also discusses the challenges of handling insulating samples, surface cleaning limitations, and the use of Ar+ and Gas Cluster Ion Beam (GCIB) for surface analysis. The lecture concludes with a summary on the identification of XPS spectrum lines, sputtering techniques, and the significance of chemical shifts in XPS analysis.