A large number of hydrological forecasting systems exist across the globe. Recent advances have pushed the limits of predictability of discharge and other hydrological variables from a few hours to several days or even months. In this chapter, we aim to give an overview of Hydrological Ensemble Prediction Systems across the globe. It provides brief descriptions of existing or preoperational systems as background, and discusses the challenges ahead. This overview shows that there is at least one system per continent, though their geographic domain varies considerably among very small catchments, countries national and interregional basins, transnational basins, continents, or even the entire globe. It highlights common challenges and differe...