This chapter discusses experimental results of surface core level shift (SCLS) of metals. From measurements of SCLS and use of the Born-Haber cycle-argument heat of segregation can be derived for an alloy. Azimuthal and polar distributions of photoelectrons from W(110), with the contributions of surface and bulk core states resolved, have been measured. Strong modulations in intensity of both contributions are observed and ascribed to photoelectron diffraction final state effects. Theoretical positions, within the microscopic model, of the XPS lines of the core level spectrum for the three low index faces of W and Ta are presented. Results of applying a fitting procedure to 4f photoelectron spectrum of W(110) are presented. Experimental ARXP spectra of the 3d bands for Cu and Ni films are illustrated. Summary of 4f core-level parameters for atoms of the first surface layer, second layer, and bulk of Ta(111), W(111), and W(100) are tabulated. The experimentally determined SCLS of the 5d transition metals with the results of different theoretical approaches is compared. Doniach-Sunjic lineshape parameters for the bulk and surface 4f emission of the lanthanides are also presented. The SCLS's with appropriate error limits are shown. The lineshape parameters can be changed 10% and 20% for the bulk and surface emission, respectively, and still yield acceptable fits. The energy scaling factor is needed to multiply the atomic theoretical multiplet splittings to get good fits of the authors' solid state spectra.