The neutron depolarization technique is based on the loss of polarization of a polarized neutron beam after transmission through ferromagnetic substances. This loss, caused by Larmor precession in individual domains, determines the mean domain size, the mean square direction cosines of the domains and the mean magnetization. The method is complementary to the neutron scattering technique with respect to the size of the inhomogeneities to be determined and the dynamic range accessible. Only the static applications of the method in studying domain structures are considered. As examples will be treated metal foils under stress, oriented ferroxdur permanent magnets, soft ferrites, recording tapes and thin films. In most of these examples magnetic correlations between neighbouring domains are subject of study.