The extragalactic background at ultraviolet, X-ray and gamma ray energies

The extragalactic background at ultraviolet, X-ray and gamma ray energies is reviewed. Early work on the diffuse backgrounds in each of these bands was motivated, at least in part, by the idea that these fluxes were the result of processes which produced a truly diffuse flux with profound cosmological implications. As we will see, these processes were not observed. However, the study of this background has led to the discovery of unexpected processes at work in the Universe. Our current understanding of these backgrounds is presented.