The ECOSIM project, first designed and implemented in 1996 was based on state-of-the-art scientific methods and information technologies that later evolved into a sophisticated but easy to use, multimedia based platform that provides decision making support on environmental planning. The integrated technologies cover a range of conditions comprised of climatic, environmental and technological based conditions such as data acquisition from environmental monitoring networks, data analysis and visualization tools, numerical simulation models (including dynamic 3D simulation models), a hybrid geographical information system, embedded expert systems and finally, strong visualisation components. All of which have been designed into a user-friendly architecture distributed through TCP/IP and http protocols. In a nutshell, the ECOSIM monitoring and modelling system aims to forecast poor air quality (in real time) and then provide a sound basis upon which decisions can be made to reduce urban air pollution and to initiate effective traffic demand management measures. There is however, a great deal more to ECOSIM than meets the eye. The integrated software tools, for example, that comprise its overall environmental modelling capacity are based on more than just air quality measuring systems. Aside from its 3D dynamic photochemical modelling tool (DYMOS) or its multi-layer dynamic photochemical tool (REGOZON) and various other tools used to monitor and model air quality, there's the POM tool, which provides a 3D costal flow and water quality analysis, and the MODFLOW tool which advances a 3D ground water flow analysis as well as the MTD-3 tool which targets groundwater quality. Additionally, ECOSIM allows for both a qualitative and a quantitative analysis of the environment, doing so in different environmental domains as well as providing dynamic interrelations between each domain. This links data of individual domains to larger scale data sources for more comprehensive model generation. Currently, ECOSIM has three validation sites; Athens, Berlin and Gdansk, although it also involves participants from the United Kingdom, Austria and Italy and it is hoped that the comprehensive data ECOSIM generates will lead to better and improved urban environmental management systems and ultimately, fewer cities with a pall of pollution poised overhead.