Three conferences on “Small Wastewater Treatment Plants” organized by the IAWQ Specialist Group demonstrate worldwide interest and activities in this matter and the need to exchange experience concerning planning, design, construction, operation, maintenance and control of small treatment plants. In near future, the number of small treatment works will increase tremendously and will be accompanied by a strong demand for information on appropriate procedures and technologies. Pollution problems caused by small wastewater flows are usually restricted to small areas, however, in view of the high per capita costs, treatment requirements and alternatives have to be studied carefully. In comparison to larger plants, more pronounced and different boundary conditions such as load fluctuations, operation and maintenance problems, per capita costs, and a large variety of feasible treatment and disposal systems ask for experienced engineers with a broad and sound knowledge in rural water quality management. The technical alternatives reaching from mechanical and simple biological low rate systems such as ponds, sand filters and reed beds to complex high rate suspended and fixed biomass reactors have to be evaluated regarding plant size, operation safety, reliability, demand for skilled personnel, investment and operation costs. In this respect, water engineers are increasingly challenged, not only to deal with a broad range of present and future treatment technologies, but also to integrate economical and social aspects into their evaluations.