This volume contains the Proceedings of a two-week NATO Advanced Study Institute on "Laser Systems for Photobiology and Photomedicine", conducted from May 11 to 20, 1990 in Erice, Italy. This is the 15th annual course of the International School of Quantum Electronics (ISQE), organized under the auspices of the "Ettore Majorana" Center for Scientific Culture. The application of lasers to medicine and surgery has made amazing progress since the last ISQE Course on this subject in 1983. The present Proceedings give a tutorial introduction to today's most important areas, as well as a review of current results by leading researchers. Among the possible approaches to a NATO Advanced Study Institute on Laser Systems for Photobiology and Photomedicine, we chose to emphasize the scientific and technological aspects of advanced laser systems when applied to laboratory and clinical tests. Since it is the policy of the School to stress the advanced scientific and techn*ological achievements in the field of Quantum Electronics, the Course broadly covers performance already achieved and potential applications.