The neutron depolarization technique is based on the change of polarization of a polarized neutron beam in three dimensions after transmission through magnetic substances. This change, caused by Larmor precession in individual domains, yields the mean domain size, the mean square direction cosines of the domains and the mean magnetization. The method is complementary to other neutron scattering techniques with respect to the size of the inhomogeneities studied, as well as the dynamic range accessible. The examples treated wil be: recording tapes, magnetic powders and superconductors.