This monograph presents a unified and coherent account of an important, focused area of rare-earth magnetism — magnetic structures and excitations — which both reflects the nature of the fundamental magnetic interactions and determines many of the characteristic properties of metals. The authors concentrate on the essential principles and their applications to typical examples, generally restricting the discussion to the pure elements and considering alloys and compounds only when they are instructive in illuminating particular topics. Both authors have been involved for some time in the effort that has been made in Denmark to study, both theoretically and experimentally, the magnetic structures and especially the excitations in the rare earths. This account of the subject represents the result of their experience, and it has been written in the hope that it will be useful not only to those who have a special interest in rare-earth magnetism, but also to a wider audience of physicists and condensed matter scientists interested in the techniques and achievements of modern research in magnetism.