Fundamental physics with cosmic gamma-rays

High energy cosmic gamma-rays are both messengers  as well as probes of fundamental physics.  The most prominent example for this close link is the search for cold dark matter via gamma-rays from self-annihilation or decay of massive particles. It is less well know that the propagation of energetic photons over cosmological distances is sensitive to effects of physics beyond the standard model which are out of reach of current and future laboratory experiments. The current observational status is summarized and possible follow-up experiments discussed.