This volume contains five reviews, mainly dealing with recent literature. These reviews are meant to introduce younger scientists into a field as well as senior scientists into related fields. The contributors and their reviews are: 1. William W. Ward: Energy Transfer Processes in Bioluminescence. After a clear and concise introduction the mechanisms of excitation and deexcitation are discussed only briefly, but references to a number of introductory and more advanced books and articles are mentioned. Reaction mechanisms in both chemiluminescence and bioluminescence are compared. Upon a short consideration of radiative and non-radiative energy transfer, bioluminescence is described for five groups of organisms. A few other partially characterized systems are mentioned as well. The energy transfer phenomenon, in particular its way of functioning in these species, is described. The review is presented in a clear and instructive way. 2. Lee H, Pratt: Phytochrome: Function and Properties. A clear and critical survey of the facts and hypotheses concerning various phytochrome reactions and properties is presented. Its purification, biochemistry and the differences between both phytochrome forms, exhibiting different morphogenic activities, as well as the localization are discussed in a most interesting way. The final chapter is very valuable, as it deals with suggestions for future research dealing with the evaluation of the many hypotheses concerning the properties and ways of functioning of phytochrome. 3. Govindjee and Paul A. Jursinic: Photosynthesis and Fast Changes in Light Emission by Green Plants. In the first chapter photosynthesis is reviewed. The major part of this chapter deals with system II reactions, as these are of primary interest with regard to the light emission phenomena. Since light emission is likely to be affected by changes in the photosynthetic membrane structure, this structure could have been discussed in some more detail. Next, a very interesting survey is presented on experiments and theories concerning chlorophyll a fluorescence and dealyed light emission. It demonstrates that many problems remain to be solved. 4. Helga Ninnemann: Photoreceptors for Circadian Rhythms. As indicated by the title, the effect of light on circadian rhythms – in both plants and animals – is considered in particular. Various action spectra are presented, whereas many data and problems concerning these rhythms are discussed in a most useful way. 5. Ronald O. Rahn: Non-dimer Damage in Deoxyribonucleic Acid Caused by Ultraviolet Radiation. In the introduction the difference between UV-induced pyrimidine dimer formation and non-dimer damage in DNA is discussed. Only the latter phenomenon is considered in more detail. Various techniques for essaying this damage, its types and effects in both plant and animal cells are reviewed in a clear way. Also here, future research is discussed. In conclusion, this volume contains a large amount of up to date information together with extensive lists of references. It therefore is most valuable to those who are interested in the reviewed fields.