  Gamma-Ray Bursts (GRBs) - short bursts of 100-1MeV photons arriving from
random directions in the sky are probably the most relativistic objects
discovered so far. Still, somehow they did not attract the attention of the
relativistic community. In this short review I discuss briefly GRB observations
and show that they lead us to the fireball model - GRBs involve macroscopic
relativistic motion with Lorentz factors of a few hundred or more. I show that
GRB sources involve, most likely, new born black holes, and their progenitors
are Supernovae or neutron star mergers. I show that both GRB progenitors and
the process of GRB itself produce gravitational radiation and I consider the
possibility of detecting this emission. Finally I show that GRBs could serve as
cosmological indicators that could teach us about the high redshift ($z \approx
5-15$) dark ages of the universe.
