It has been firmly established that the atom-projected d-band center of mass of transition metal systems, is a good descriptor of surface local chemical reactivity. Any surface modification, like alloying, atomic coordination changes and adsorption processes, brings about shifts of the d-band center of mass. Surface Core Levels (SCLs), as measured by High Resolution X-Ray Photoelectron Spectroscopy, shift almost rigidly with the center of the d-band, and provide therefore a measure of local surface reactivity changes. I will present a number of examples which illustrate this paradigm. In particular, I will present SCL shifts measurements originating from Rh atoms, with coordination number varying between 3 and 12, and SCL shifts originating from Rh, Pt and PtRh surfaces, upon adsorption of O, H, N and CO species. I will show that the energy shifts and intensity changes of time-lapsed SCL spectral components, contain information from which the kinetics and dynamics of surface processes can be direcly determined. For each of the presented systems, DFT calculations show that SCL shifts provide a good spectroscopic descriptor of local surface chemical reactivity changes.