The pollution of water resources by man's domestic waste, his industry, his agriculture and other activities is experienced in all parts of the world. This pollution is an inevitable accompaniment of population expansion, burgeoning industry, increasing urbanization and a surge toward a higher standard of living. The Second International Conference on Water Pollution Research held in Tokyo in August 1964 provided and opportunity for a pooling of knowledge on recent research in water pollution control, and for an examination of the perspectives offered to both the scientifically advanced and the developing countries of the world. Three areas of research activity of outstanding interest were highlighted: freshwater pollution, waste treatment, and marine waste disposal. Through 48 technical papers and 140 formal discussions, the activities of engineers, biologists, chemists, microbiologists, limnologists, oceanographers, and other scientists were described, examined, and evaluated. The Second International Conference on Water Pollution Research, like the First Conference held in London in 1962, gives the field of water pollution control the fruit of the laboratory and field study endeavors of engineers and scientists highly motivated toward obtaining information essential to cleansing their Nation's water Resources. These papers and discussions, together with the questions and their answers, and the informal commentary from the floor, provide research workers with a clearer focussing of significant research needs, new approaches to ways of solving difficult problems, and an elevated base from which to initiate new research programs. The papers and discussions contained in these volumes will be useful wherever research in water poollution control is being planned and conducted. They represent the effort of many of the world's leading research workers in water pollution control, particularly during the period 1962-1964.