Hydropower is the largest single renewable electricity source today, providing 16% of world electricity at competitive prices. It dominates the electricity mix in several countries, developed, emerging or developing. In many others it provides significant amounts of clean, renewable electricity. It also helps control water flows and availability. Its extreme flexibility is a strong asset for electric systems, and will be vital to accommodate and facilitate the growth of variable renewable energy technologies such as wind power and solar photovoltaics. It can foster social and economic progress, especially in developing countries. This roadmap considers that both annual hydropower capacities and generation should by 2050 roughly double from current levels.