MIKE BASIN is a versatile GIS-based water resource and environmental modelling package. It provides a simple, yet powerful framework for managers and stakeholders to address multi-sectoral allocation and discharge issues in a river basin. MIKE BASIN represents all elements of water resource modelling: users, reservoirs, hydropower, surface water, groundwater, rainfall-runoff, and water quality. Its object-oriented and open-ended code allows users to write their own Visual Basic rules, and make their own decision support interfaces in e.g. Microsoft Excel. MIKE BASIN uses the full strength of GIS and database integration and is ideal for communicating with non-technical audiences.