H. J. BEYER AND H. KLEINPOPPEN During the preparation of Parts A and B of Progress in Atomic Spectros­ copy a few years ago, it soon became obvious that a comprehensive review and description of this field of modern atomic physics could not be achieved within the limitations of a two-volume book. While it was possible to include a large variety of spectroscopic methods, inevitably some fields had to be cut short or left out altogether. Other fields have developed so rapidly that they demand full cover in an additional volume. One of the major problems, already encountered during the prepar­ ation of the first volumes, was to keep track of new developments and approaches which result in spectroscopic data. We have to look far beyond the area of traditional atomic spectroscopy since methods of atomic and ion collision physics, nuclear physics, and even particle physics all make important contributions to our knowledge of the static and dynamical state of atoms and ions, and thereby greatly add to the continuing fascination of a field of research which has given us so much fundamental knowledge since the middle of the last century. In this volume, we have tried to strike a balance between contribu­ tions belonging to the more established fields of atomic structure and spectroscopy and those fields where atomic spectroscopy overlaps with other areas.