Article Outline Acknowledgements References The EU Water Framework Directive (WFD) by the European Commission is the major concept for achieving sustainable management of water in EU Member States. Next to treatment of coastal waters, it requires that all inland waters within defined river basins must reach at least good status by 2015. This also requires a constantly improved understanding of physical, chemical and biological processes of pollutants for the assessment of current and future quality of surface- and groundwater bodies. As a driving force for concepts such as the WFD, the EU project AquaTerra aims at a better understanding of pollutants in the river–sediment–soil–groundwater systems as a whole. This involves quantification of key pollutants and understanding of their turnover. The work also leads to the development of new numerical models, which are needed to predict adverse trends in soil functioning, water quantity and quality. Scales range from water–solid interactions to transport of dissolved and suspended matter at the river basin scale. This approach provides the foundations for improved river basin management, enhanced soil and groundwater monitoring programs and the early identification and forecasting of impacts on water quantity and quality. AquaTerra is among the largest environmental projects worldwide with a multidisciplinary team of 45 partner organisations. The work integrates across various disciplines that range from Geosciences, Environmental Engineering and Physics, Biology and Chemistry to Socio-Economic sciences. It also involves practitioners and end users such as policy makers, river basin managers and regional as well as urban land planners. This special issue presents a selection of key results of AquaTerra from sites in the river basins of the Ebro, Meuse, Elbe and Danube and from the small French catchment of the Brévilles Spring. The presented papers treat aspects of surface- and groundwater interaction (Rozemeijer and Broers; Petelet-Giraud et al., ms #1 and #2) and sediment transport (Klaver et al., ms #3). Other studies address the mobility and turnover of organic pollutants such as pesticides (Baran et al., ms #4) and polyaromatic hydrocarbons (Morasch et al., ms #5) and several manuscripts deal with metal behaviour in soils, sediments and floodplains (Joubert et al.; Vanbroekhoven et al.; Barborowski et al.; Poot et al.; Graf et al., ms #6 to #10). Further contributions to this special issue focus on field and laboratory techniques such as groundwater dating (Visser et al., ms #11), integral pumping tests (Kalbus et al., ms #12), and new aspects of biomonitoring (Hsu et al.; Bleeker and Van Geestel, ms #13 and #14). The modelling studies presented here quantify ecotoxicological aspects (Vink and Meeussen, ms #15) and outline surface- and groundwater hydrology in the context of climate change (Bürger et al.; Kolditz et al., ms #16 and #17) and the special issue closes with considerations on challenges to link science with policy (Slob et al., ms #18). Apart from these selected publications, comparative work between basins included collection and processing of close to 2000 soil, sediment, surface- and groundwater samples. Regional activities included a detailed survey of the Danube that covered a 1147-km stretch of the river. In the Ebro, sediment and fish samples from selected risk zones were analysed for a variety of emerging pollutants and led to the detection of the flame retardant decabromodiphenylethane that was unknown before in the area. On the other hand, mobilisation and turnover of β-hexachlorohexane was quantified in the Elbe Basin. New laboratory methods included validations of analytical procedures for alachlor, metalochlor, acetochlor and its ethanesulfonic and oxanilic acids and hexabromocyclododecane in aqueous samples. Other laboratory studies in AquaTerra have characterised colloids and dissolved organic matter and associated contaminant transport. New sorption isotherms for compounds including phenanthrene, naphthalene and atrazine were also established for selected reference materials and soils. This was further combined with microbiological degradation tests of compounds including atrazine, nonylphenol, dichlorodiphenyltrichloroethane (DDT), vinylchloride, 1,2-dichloroethane, methyl tert butylethers (MtBE), chlorobenzene, chloroanilines, brominated flame retardants and PAHs. Other new modelling activities in AquaTerra have generated synthetic rainfall time series that were further processed in hydrological models. In addition, new developments of software for data viewing included implementation of 3D visualization methods for catchment applications. For modelling entire river basins, data from historical pollution from agriculture, industry and sewage were combined with GIS methods to assess for instance the Ebro River environmental quality. The above summary and this special issue only present selected aspects of AquaTerra, but provide a good insight into its achievements. More details can be found under http://www.eu-aquaterra.de/ with its growing list of peer-reviewed publications and in some overview publications about the project ([Barth and Fowler, 2005], [Barth and Grathwohl, 2006] and [Gerzabek et al., 2007]).