  Despite the dramatic improvement of our knowledge of the phenomenology of
Gamma Ray Bursts, we still do not know several fundamental aspects of their
physics. One of the puzzles concerns the nature of the radiative process
originating the prompt phase radiation. Although the synchrotron process
qualifies itself as a natural candidate, it faces severe problems, and many
efforts have been done looking for alternatives. These, however, suffer from
other problems, and there is no general consensus yet on a specific radiation
mechanism.
