Gamma-Ray Bursts Polarization

We review the current observational and theoretical status of the polarization measurements of Gamma-ray Bursts at all wavelengths. Gamma-Ray Bursts are thought to be produced by an ultra-relativistic jet, possibly powered by a black hole. One of the most important open point is the composition of the jet: the energy may be carried out from the central source either as kinetic energy (of baryons and/or pairs), or in electromagnetic form (Poynting flux). The polarization properties are expected to help disentangling main energy carrier. The prompt emission and afterglow polarization are also a powerful diagnostic of the jet geometry.