The choice of title for this collective volume reflects the desire of the editors and authors to make clear that, while the bulk of the material is concerned with luminescence, other aspects of the excited state have not been excluded. In the five years which have elapsed since the publication of the classical monograph of Konev, a wealth of new information has ap­ peared on the emission properties of proteins and nucleic acids. Indeed, since new publications in this area appear to be proliferating in a geometric ratio, this may be the last opportunity to provide a comprehensive summary of the field in a book which is not of prohibitive length. This is what we have attempted to do here. While the orientation of each chapter naturally reflects the interests and point of view of the author, there has been a general effort to present .a critical assessment of existing results and interpretations, rather than a compendium of data with minimal comment. Finally, it should be stressed that the rapid evolution of the subject at the time of writing makes it inevitable that the book will age to some degree over the next few years, although this will occur at differing rates for the various chapters. We can only hope that most of the material in this interim summing-up will prove resistant to the erosion of time and provide a solid foundation for further progress.