Raman Spectroscopy, Volume 1, was conceived to provide integrated and comprehensive coverage of all aspects of the field by a group of specialists. However, in the three years since the first volume was published much important work has been done. Since Volume 1 was very well received, this second volume has been prepared in the belief that an extension of the coverage it offers will satisfy a real need in this rapidly changing and extremely interesting field. Any pretension to comprehensive coverage, however, had to be abandoned. In order to keep the material in a work of this nature up to date, a cutoff date has to be set. Inevitably one or two of the planned articles fail to materialize by this deadline, and other interesting topics may come into focus too late to permit the preparation of a worthwhile discussion by the target date. Still, in fairness to those authors who kept to the schedule, the cutoff date has to be enforced, even though this means sacrificing breadth of coverage to timeliness. I wish to thank all the contributors to this volume for their effort, their cooperation, and their punctuality, and it is my hope that the policy I have followed will result in the presentation of current thought on a series of interesting aspects of the subject of Raman spectroscopy. May 1970 H.A.S. Contents Chapter 1 Vibrational Rules of Selection and Polarization: Their Practical Uses and Limitations .................... .