Since the great discovery made by Laue, x-ray diffraction has become the most im­ portant method for the investigation of atomic structure in condensed matter. Cer­ tain investigations, however, are difficult or totally impossible to conduct using x-rays, for example, the localization of atomic nuclei or atoms having only a few core electrons, and the observation of magnetic moments. The investigation of these important areas is made possible by neutron diffraction. Thus this method has developed into an important supplement to x-ray investigations. An ever-increasing de­ mand is put on the method by research areas, old and new. Neutron diffraction has completely reformed the subject of solid-state magnetism; especially the area of chemical binding has received a new impetus by the union of x-ray and neutron dif­ fraction. An exchange of different isotopes of the same element gives rise, as a rule, to a change in the strength of the neutron diffraction. Due to this effect itls possible, by means of deuteration, to make visible a single chain in a solid high polymer. Thus neutron small-angle scattering is important in protein research and for the biology of macromolecules. Of equal importance is the application of neu:ron diffraction in metallurgy. There already exist several excellent books which discuss the results obtained by neans of neutron diffraction.