The subject of this book is the examination of structural and magnetic properties of ultrathin metal films on metal oxide substrates by means of grazing-incidence small-angle x-ray scattering (GISAXS), low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and conversion electron Mößbauer spectroscopy (CEMS). Two systems were investigated, namely five monolayers of iron on polished MgO(001), and two and five monolayers of gold on Fe3O4(001). These are of common interest due to their catalytic properties and their importance for microelectronics.