The objective of the Specialist Group (SG) is to address and promote all aspects of modelling, simulation and the formal methods of applying systems analysis to managing and improving the quality of the aquatic environment. The Modelling and Integrated Assessment (MIA) SG targets people from research, consulting companies, institutions and operators to consider and apply the use of models and computing tools to support the understanding, management and optimisation of water systems. This includes the development and application of mathematical models and modelling tools, such as optimisation algorithms, time-series analysis and forecasting, computational procedures for decision analysis and support, uncertainty analysis… It hereby stimulates transfer of knowledge between academia and industry and between different areas within the water cycle. The Group is also responsible for maintaining a forum for the discussion of inter-disciplinary issues within the IWA to augment the engineering and economic elements of problem-solving with those having human, institutional and cultural dimensions to them. The SG is also directed, therefore, at developing and promoting the application of systematic procedures for Integrated Assessment.