Floods affect more people worldwide than any other natural hazard. With more than $ 100 Bn average annual losses, floods are of high relevance for society and economy. Current approaches for assessing flood risk often ignore interactions and changes in the atmosphere, catchments, river-floodplains, and socio-economic systems. As a consequence, risk analyses are uncertain and might be biased. However, reliable risk estimates are needed to prioritize investments in flood risk mitigation and for the insurance sector. To advance this field, the Marie Skłodowska-Curie European Training Network SYSTEM-RISK works on ‘A large-scale systems approach to flood risk assessment and management’. SYSTEM-RISK research considers the complete chain of processes involved from the meteorological events to the consequences, the manifold interactions, and temporal changes in flood risk systems. It focuses on the Atmosphere-Catchment System, the River-Dike-Floodplain System and the Socio-Economic System. Novel tools are developed for implementing the systems approach which allows considering upstream-downstream interactions within river systems, for instance, due to levee breaches, taking into account temporal changes in risk, such as the effect of private precaution on flood losses, and processing big data volumes and simulating large-scale yet high-resolution floods. These novel tools allow to comprehensively consider flood risk drivers, to understand and factor in human behaviour, to improve the integration of actors in risk management practice, to quantify the spatial redistribution of risk on large scales, and to assess risk management strategies in terms of risk reduction and equity in risk distribution. The close exchange between scientists and policy-makers, flood risk managers and private stakeholders makes sure that risk management practice can profit from the System-Risk perspective.