The planning, design and operation of urban drainage systems (UDS) is a domain of civil engineers. Whereas technical progress in planning and design was strongly stim ulated by research and development, the operational problems have received comparatively little attention. Since an increasing num ber of UDS are equipped with sensors and data collection systems, knowledge is being gained of actual operational performance. Appropriate control systems (i.e. hardware) and control strategies (i.e. software) are being developed in order to use the existing systems better and to increase UDS performance to the maximum. In 1986 the IAWPRC/IAHR Joint Committee on Urban Storm Drainage commissioned a group of engineers and scientists to study the technical developments in the field of realtime control of urban drainage systems (RTCUDS). Initially the task group focused on the compilation of the present knowledge on RTCUDS. The result is this state-of-the-art report. It is planned to keep the report up-to-date and, ultimately, extend it so that it can be used as a RTCUDS planning, design and operations handbook.