X-ray emission results as material falls (accretes) in a strong gravitational field. We analyzed a huge number of X-ray spectra from accretion onto stellar remnant black holes to build a theoretical understanding of the bewildering variety of behaviors seen. These models are also able to explain the accreting neutron star systems, where the differences imply that black holes really do have an event horizon rather than a solid surface! I will describe we can build a coherent picture of accretion in stellar mass objects and how this can be extended to give insights into the supermassive black hole accretion which power the Quasars and Active Galactic Nuclei