  Gamma-Ray Bursts (GRBs) have remained a puzzle for many high-energy
astrophysicists since their discovery in 1967. With the advent of the X-ray
satellites BeppoSAX and RossiXTE, it has been possible to carry out deep
multi-wavelength observations of the counterparts associated with the GRBs just
within a few hours of occurence, thanks to the observation of the fading X-ray
emission that follows the more energetic gamma-ray photons once the GRB event
has ended. The fact that this emission (the afterglow) extends at longer
wavelengths, has led to the discovery of the first optical/IR/radio
counterparts in 1997-98, greatly improving our understanding of these sources.
Now it is widely accepted that GRBs originate at cosmological distances but
while the observed afterglow satisfies the predictions of the relativistic
fireball models, the central engines that power these extraordinary events
remain still unknown. Detailed results for nine selected GRBs are presented as
well as a summary of the GRB counterparts and host galaxies found so far.
