  Gamma-ray bursts (GRBs) are most intense transient gamma-ray events in the
sky when they are on together with the strong evidences (i.e. the isotropic and
inhomogeneous distribution of GRBs detected by BASTE) that they are located at
cosmological distances, which make them the most energetic events ever known.
For example, the observed radiation energies of some GRBs are equivalent to
convert more than one solar mass energy into radiation completely. This is
thousand times stronger than that of supernova explosion. Unconventional energy
mechanisms and extremely high conversion efficiency for these mysterious events
are required. The discovery of host galaxies and association with supernovae in
the cosmological distances by the recently launched satellite of BeppoSAX and
ground based radio and optical telescopes in GRB afterglow provides further
support to the cosmological origin of GRBs and put strong constraints on
central engines of GRBs. It is the aim of this article to review the possible
central engines, energy mechanisms, dynamical and spectral evolution of GRBs,
especially focusing on the afterglows in multi-wavebands.
