The major theme of the International Biohydrometallurgy Symposium IBS-99 'Biohydrometallurgy and the Environment toward the mining of the 21st Century', held in El Escorial (Spain) from 20-23 June 1999, is biohydrometallurgy and the environment since it is predicted that in the coming century biotechnology will make its greatest contribution in this area. From the papers in these volumes it is clear that environmental issues are already of great interest to the biohydrometallurgical community. Although all the classical biohydrometallurgical topics - e.g. bioleaching, microbiology, molecular biology, biosorption, bioremediation - are addressed, the continued emphasis is on the environmentally friendly aspects of the biotechnologies used. Given the interdisciplinary nature of the field, biologists, hydrometallurgists, geologists, chemists, physicists and engineers should be interested in this collection of papers which discuss the future trends in biohydrometallurgy.