  High-energy photons (above the MeV) are a powerful probe for astrophysics and
for fundamental physics under extreme conditions. During the recent years, our
knowledge of the high-energy gamma-ray sky has impressively progressed thanks
to the advent of new detectors for cosmic gamma rays, at ground (H.E.S.S.,
MAGIC, VERITAS, HAWC) and in space (AGILE, Fermi). This presentation reviews
the present status of the studies of fundamental physics problems with
high-energy gamma rays, and discusses the expected experimental developments.
