The diffuse extragalactic background radiation (DEBRA) refers to the diffuse photon field from extragalactic origin that fills our Universe. It contains photons over ∼20 decades of energy from ~10−7 eV to ~100 GeV. The origin and the physical processes involved are different within every wavelength range. There is plenty of observational evidence that support the existence of the DEBRA.The figure shows a schematic picture, based on many different data sets, of the spectral intensity (also called spectral radiance) multiplied by wavelength of the DEBRA over all the electromagnetic spectrum. This representation is convenient because the area inside the curve is the energy. The nature and history of the universe is coded in this radiation field and any realistic cosmological model must be abl