  The gamma-ray background is still a subject under great debate.
  All phenomena in the universe emitting gamma-rays can contribute directly as
diffuse emission or as an isotropic component from unresolved point sources.
The question of the origin of the extragalactic component cannot be answered
without determining the galactic emission. To discuss in detail all models
resulting in gamma-ray background contributions is far beyond the scope of this
paper. Therefore the focus will be on recent publications on the extragalactic
high energy (>100 MeV) part of the gamma-ray background.
