There is a great lack of proper wastewater treatment in developing countries. With respect to the environment this situation should be changed as fast as possible. Due to the financial situation and to the more stringent standards, wastewater sewerage and treatment are much more developed in industrialized countries. Consequently there is an enormous pool of experience and knowledge in these countries with a lot of different systems based on scientific and practical work. One of the most promising technologies for application in developing countries seems to be constructed wetlands (CW), due to their characteristic properties like utilization of natural processes, simple construction, simple operation and maintenance (O/M), process stability, cost effectiveness, etc. Our Institute has been dealing a lot with CW and now feels obliged to transfer its know-how in this field to developing countries to help them in solving their problems. At the moment we are cooperating with the following countries: China, Kenya, Mexico, Nepal, Nicaragua, Tanzania and Uganda. Different ways are being followed to realize this together with several organisations and partners. The paper will deal with these cooperative arrangements in detail, demonstrating different projects, describing the procedures in the projects, discussing experiences and last but not least giving recommendations for future optimum ways of proceeding.