W. HANLE and H. KLEINPOPPEN In 1919, in the first edition of Atombau and Spektrallinien, Sommerfeld referred to the immense amount of information which had been accumu lated during the first period of 60 years of spectroscopic practice. Sommer feld emphasized that the names of Planck and Bohr would be connected forever with the efforts that had been made to understand the physics and the theory of spectral lines. Another period of almost 60 years has elapsed since the first edition of Sommerfeld's famous monograph. As the editors of this monograph, Progress in Atomic Spectroscopy, we feel that the present period is best characterized by the large variety of new spec troscopic methods that have been invented in the last decades. Spectroscopy has always been involved in the field of research on atomic structure and the interaction of light and atoms. The development of new spectroscopic methods (i.e., new as compared to the traditional optical methods) has led to many outstanding achievements, which, together with the increase of activity over the last decades, appear as a kind of renaissance of atomic spectroscopy."

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."

W. HANLE and H. KLEINPOPPEN In 1919, in the first edition of Atombau and Spektrallinien, Sommerfeld referred to the immense amount of information which had been accumu lated during the first period of 60 years of spectroscopic practice. Sommer feld emphasized that the names of Planck and Bohr would be connected forever with the efforts that had been made to understand the physics and the theory of spectral lines. Another period of almost 60 years has elapsed since the first edition of Sommerfeld's famous monograph. As the editors of this monograph, Progress in Atomic Spectroscopy, we feel that the present period is best characterized by the large variety of new spec troscopic methods that have been invented in the last decades. Spectroscopy has always been involved in the field of research on atomic structure and the interaction of light and atoms. The development of new spectroscopic methods (i.e., new as compared to the traditional optical methods) has led to many outstanding achievements, which, together with the increase of activity over the last decades, appear as a kind of renaissance of atomic spectroscopy."