The World Water Congress held in Paris in July 2000 was the first under the banner of the International Water Association, formed by the merger of the International Association on Water Quality and the International Water Services Association. The success of the merger was reflected in the unprecedented degree of interest and participation in the Congress, with nearly two-and-a-half thousand delegates attending for 450 oral presentations, 750 poster presentations and 4 workshops and seminars. From the large number of oral presentations in both the operations and management and the scientific and technical sessions, 58 papers dealing with aspects of the management of water, wastewater and solids have been selected for this issue. Topics include: wastewater operational methods and tools; economic optimization and management; industrial wastewater treatment; small wastewater treatment plants; aeration in wastewater treatment; nuisance-free wastewater treatment plants; sewerage management; watershed and water resources management; landfill management of solid wastes; sludge characteristics; and sludge management. With authors who rank among the world's leading experts in these fields, tackling some of the most prominent contemporary problems, these proceedings are an essential compilation of the latest advances in the management of water, wastewater, the associated solid wastes, and the utilities responsible for these tasks.