The development of a general applicable model for the analysis of water demand and allocation problems in river basins was initiated by Dr Robert J. Verhaeghe and Wil N.M. van der Krogt MSc in 1985 in the framework of the "Tana and Athi river morphology Study for the Tana and Athi River Development Authority, Nairobi". The River Basin Simulation Model RIBASIM Version 1.00 software was one of the deliverables of the Tana and Athi River basin project. The project was directly followed by two long-term innovative water resources planning and cooperation projects in which new requirements and insights on the use of river basin planning software could be further developed and applied. One project was the “Cisadane-Cimanuk Integrated Water Resources Development project (1986-1989, BTA-155)" in Indonesia. The second project was the study on the "Preparation of a national masterplan for water resources management of Taiwan". Since then a continuous need for the use of the RIBASIM software in many projects started. New requirements on river basin modelling, applications, user-interface, operating system, data collection and processing of large data sets leads to a continuous development which still lasts. RIBASIM has been applied in many countries and river basin worldwide. Many from Deltares (previously Delft Hydraulics) and from outside Deltares contributed to the application and development of RIBASIM.