Abstract: The review is focused on the use of small-angle polarized-neutron diffraction to describe the orientation of local magnetization vector in spatially ordered magnetic metamaterials. The objects of study are direct and inverse opals; these materials are synthesized for diverse applications in magnetooptics, micro- and nanoelectronics, and photonics. The methodology of experiments and the theoretical base for processing experimental results are considered in detail. It is shown that the method of small-angle diffraction of polarized neutrons is unique in solving such problems; it is used at the limit of its possibilities when studying the magnetic structure under an applied field on the scale of ~400–800 nm. The questions of frustration of local magnetization vectors are discussed using the structural data on direct and inverse opals, obtained by ultra-small-angle diffraction of synchrotron radiation. The existing methods for synthesizing direct and inverse opals, which make it possible to obtain metamaterials with a three-dimensional ordered structure of nanoparticles, are also described.