Floods are the most common cause of weather-related disasters globally, causing billions of dollars’ worth of damage and the loss of hundreds of thousands of lives. Flood early warning systems can significantly reduce the devastating impacts of floods on lives and livelihoods for the poorest and most vulnerable. To do so, they must be ‘end-to-end’, combining risk knowledge, risk monitoring, communication and dissemination, and the ability to respond. In 2016, the United Nations Office for Disaster Risk Reduction will produce guidelines that will shape how the Sendai Framework for Disaster Risk Reduction 2015–2030 is implemented around the world with regard to early warning systems. These guidelines must demand end-to-end systems that deliver actionable information to those most vulnerable to floods.