  The polarization of the optical afterglow (AG) of Gamma-Ray Bursts (GRBs) has
only been measured in a few instances at various times after the GRB. In all
cases except the best measured one (GRB 030329) the observed polarization and
its evolution are simple and easy to explain in the most naive version of the
"Cannonball'' model of GRBs: the "intrinsic" AG polarization is small and the
observations reflect the "foreground" effects of the host galaxy and ours. The
polarization observed in GRB 030329 behaves chaotically, its understanding
requires reasonable but ad-hoc ingredients. The polarization of the gamma rays
of a GRB has only been measured in the case of GRB 021206. The result is
debated, but similar measurements would be crucial to the determination of the
GRB-generating mechanism.
