The iEMSs 2004 Conference includes research contributions from environmental modellers and software developers and users. It encouraged contributors to address a topical theme that is very relevant for the iEMSs: Complexity and integrated resources management. Special emphasis is given to the analysis and modelling of complex human-technology-environment systems and the implications of complexity and uncertainty for management concepts and decision making. Contributions discuss new concepts, methodologies and tools and explore the current state of the art in various application areas of high scientific, social, economic and political relevance. The conference was coordinated with the preceding international symposium Uncertainty and Precaution in Environmental Management (7-9 June 2004, Copenhagen).