After many years of fruitless research on primary γ-Rays, the results obtained by Clark et al.  with the OSO-3 satellite, proved for the first time the existence of a primary γ-Ray flux. The study of the distribution of this radiation showed a strong anisotropy in the direction of the galactic disk and, more precisely, in the direction of the galactic center. Now the production of γ-Rays in the spatial medium is related to high energy processes and to the presence of relativistic electrons. The high energy processes bring about an emission of γ-Rays essentially by decay of the π° mesons created for instance, by the interaction of cosmic radiation with interstellar matter or by matter-antimatter annihilation. The relativistic electrons can lead to an emission of γ-Rays by various processes: in particular, by bremsstrahlung of the electrons in the interstellar matter or by the Inverse Compton effect with the photons of the stellar light or of the infrared radiation background.