The main theme of this symposium was the application of chemical methods for water and wastewater treatment and their effect on the environment. The participants represented many countries and many disciplines and, taken together, their papers provide a very interesting overview of the way in which chemical processes are used in different parts of the world. The contributions from the USA are mainly devoted to methods for reducing the environmental hazard of alternative energy sources such as oil shales and tar sands. A fresh interest in coal and lignite is also apparent in the papers from Canada and from western and eastern Europe. Many papers and discussions deal with the related technology of desulphurisation of coal and oil during combustion or in exhaust gases, much of the research in this area being inspired by the problems of acid rain and the damage to forests in the northern hemisphere.