Other than electromagnetic waves, thermal neutrons interact not with the electron shell of the atoms, but with the nuclei themselves. There is no obvious regularity across the periodic system of elements: even isotopes of the same element may display big differences in contrast. Neutrons penetrate most metals easily, while hydrogen delivers huge contrast. This makes neutron imaging a tool that delivers information complementary to X-rays. As magnetic particles, neutron beams can be polarized to give information about magnetic structures. The talk will illustrate the generation of thermal neutron beams, possibilities, but also limitations of neutron imaging.