Th i s book had its orl gl n in the sympos i urn on "Polymers for Desalination" sponsored by the Division of Polymer Chemistry of the American Chemical Society and held in September, 1971 in Wash­ ington D. C. at the 162nd national meeting of the Society. However, the book is not simply the proceedings of that symposium. A number of additional papers were contributed by other workers in the field, and the original papers presented at the symposium have, for the most part, been expanded. The book thus represents a broad cross section of membrane research and development activities in the United States and abroad within the field of reverse osmosis. The purposes of the book are to bring attention to important new developments in this field, to suggest what the next generation of reverse osmosis equipment may look like, and to indicate where fur­ ther research and development are needed. The vast majority of the papers collected here represent work supported by the Office of Saline Water of the United States Department of the Interior, and the emphasis here is clearly on the application of the reverse os­ mosis process to water purification. However, many of the concepts, methods, and conclusions are expected to be useful in other areas of membrane science and technology.