Investigations on the specific effects of blue light on plants began some fifty years ago. In re cent years the growing awareness of blue-light-in- duced phenomena in plants, microorganisms, and animals has accelerat- ed and expanded this research into an ever-increasing variety of blue- light effects in biological systems. In 1977, J .A. Schiff and W .R. Briggs proposed a specific meeting to present and summarize the various blue-light effects and to discuss their mechanisms and possible photoreceptors. In view of the variety of re- sponses and the range of organisms affected by blue light the term Blue Light Syndrome seemed to be the only appropriate one for the meeting. With the help of the International Advisory Committee (W.R. Briggs, Stanford; J. Gressel, Rehovot; W. Kowallik, Bielefeld; S. Miyachi, To- kyo; W. Rau, Munich, and J.A. Schiff, Waltham), and the very generous financial support provided by the Deutsche Forschungsgemeinschaft as well as by the Bundesministerium für Forschung und Technologie, the Kultusminister des Landes Hessen, and the Philipps-Universität Marburg, the "International Conference on the Effect of Blue Light in Plants and Microorganisms" was held in July 1979 in the Philipps-Universität Mar- burg.