The extragalactic diffuse emission at -ray energies has interesting cosmological implications since the bulk of these photons suffer little or no attenuation during their propagation from the site of origin. Before the launch of the Compton Gamma-Ray Observatory (CGRO), several balloon experiments (White et al. 1977; Schönfelder et al. 1980) and the -ray spectrometer flown aboard three Apollo flights (Trombka et al. 1977) showed the presence of a feature in the few MeV range, that was in excess of the extrapolated hard X-ray continuum. At higher energies, above 35 MeV, the SAS-2 satellite provided the first clear evidence for the existence of an extragalactic -ray component (Fichtel et al. 1975).
The first all-sky survey in low energy -rays (1 MeV - 30 MeV) has been performed by COMPTEL and at higher energies, above 30 MeV, by EGRET on board CGRO. The improved sensitivity, low instrumental background and a large field of view of these instruments have resulted in significantly improved measurements of the extragalactic -ray background. In the following I shall briefly summarize the recent analysis results, and then I shall discuss the implications of these new findings on the origin of the extragalactic diffuse emission and current models thereof.