Modelling Aspects of Water Framework Directive Implementation: Volume 1 is a concrete outcome from the Harmoni-CA concerted action as part of a 4-volume series of Guidance Reports that guide water professionals through the implementation process of the Water Framework Directive, with a focus on the use of ICT-tools (and in particular modelling). They are complementary to the Guidance Documents produced by the EU Directorate General for Environment.Water resources planning and management and the development of appropriate policies require methodologies and tools that are able to support systematic, integrative and multidisciplinary assessments at various scales. It also requires the quantification of various uncertainties in both data and models, and the incorporation of stakeholders participation and institutional mechanisms into the various tools and risk assessment methodologies, to help decision makers understand and evaluate alternative measures and decisions.The other three volumes in the series are:Water Framework Directive: Model supported Implementation - A Water Manager's Guide edited by Fred Hattermann and Zbigniew W KundzewiczIntegrated Assessment for WFD implementation: Data, economic and human dimension - Volume 2, edited by Peter A. Vanrolleghem.Decision support for WFD implementation - Volume 3, edited by Peter A. Vanrolleghem.