The idea for an international symposium on regulated streams was conceived over an open-faced sandwich at the R&dhus in Copenhagen when we attended the Congress of the Societas Internationalis Lim nologiae in summer 1977. Although* we were aware that various col leagues were working on ecological problems in reservoir tailwaters, we did not fully comprehend the magnitude of worldwide stream regu lation nor the extent of interest in the subject. Such revelations are reflected in the 21 papers included in this book. The authors have summarized current understanding of the ecology of regulated streams and attempted to convey the importance and direction of future scientific investigations in stream ecosystems altered by upstream impoundments. The First International Symposium on Regulated Streams was the plenary event at the 27th annual meeting of the North American Benthological Society, April 18-20, 1979, in Erie, Pennsylvania. More than 500 colleagues attended. We gratefully acknowledge the support granted by the National Science Foundation; these funds permitted intellectual exchange between scientists from eight coun tries on four continents. We extend personal thanks to Dr. K. W. Stewart, President of NABS, and the NABS Program Committee, including Drs. E. C. Masteller, E. R. Brezina, and W. P. Kovalak. These individuals and other officers and members of the Executive Committee assisted us with the many details leading to organization and staging of a scientific forum. Discussions with Dr. John Cairns, Jr. and Dr. G. Richard Marzolf during the early planning stage were most helpful.