The electronic structure of the oxides Pb02, In203, PbO and Bh03 have been studied using high resolution X-ray photoelectron spectroscopy (XPS), ultra-violet photoemission spectroscopy (UPS), hard X-ray photoelectron spectroscopy (HXPS), and X-ray emission (XES). These techniques are supported by band structure calculations carried out within the framework of density functional theory (DFT). It has been demonstrated using UPS, XPS and HXPS that the metallic nature l Trinity Term 2008. David J. Payne Submitted for the degree of Doctor of Philosophy Trinity College, Oxford. ,. ~!II ItI \IfI [l I ofPb02 arises from the occupation of conduction band states above the Fermi level of stoichiometric Pb02, most likely arising from oxygen vacancy defects. XPS and HXPS studies of the Pb 4/ core line show that strong satellites are observed at an energy consistent with the plasmon frequency observed in electron energy loss spectra. These satellites are not present in UPS measurements of the Pb 5d core line. It has been shown using XPS, HXPS, XES and DFT that the fundamental band gap for In203 is much smaller than the often quoted value of 3.75 eV. The fundamental band gap is direct, but direct optical transitions give minimal intensity until 0.81 eV below the valence band maximum. The results are consistent with a fundamental bandgap in the region of2.67eV. Structural distortions in post-transition metal oxides are often explained in terms of the influence of sp hybrid 'lone pairs'. XPS and XES measurements on a- PbO and a-Bh03 show that this model must be revised. A high density of metal 6s states is observed at the bottom of the valence band, and would therefore be unable to directly participate in hybridization with metal 6p states which lie above the valence band. These measurements are consistent with the results of density functional theory calculations.