GENIE, the Geneva Environmental Information System, is a modular information and decision support system that is being developed at the University of Geneva under the auspices of the Centre Universitaire d'Ecologie Humaine in collaboration with: the Laboratory of Plant Biochemistry and Physiology, the HEC Logilab group, the Département de Géographie, the Groupe des Sciences de la Terre, the Conservatoire et Jardin botaniques de la Ville de Genève and Laboratoire Universitaire de biosystématique et floristique. GENIE aims at providing an easily accessible and easy to use, but highly integrated repository of environmental information and decision support tools. Designed as a distributed system based on a flexible client-server architecture, it brings together various and distributed data and information resources In addition to descriptive information, the system also provides tools for WHAT-IF analysis, supporting the design and analysis of scenarios of environmental planning, management and policy, by forecasting the impacts of potential actions. While the system will eventually address the full range of urban and regional environmental problems, the first implementation concentrates on air quality assessment and management, and the energy and transportation sectors as the main sources of emissions.