The capacity of hydroelectric systems to reach maximum production from zero in a rapid and foreseeable manner makes them exceptionally appropriate for addressing alterations in the consumption and providing ancillary services to the electricity system, thus maintaining the balance between the electricity supply and demand. Hydropower does not only provide clean energy but also helps in the process of fighting climate change. This course deals with the generation of power derived from running water or water stored in dams. It addresses the availability of the resources, the capabilities and limitations of the types of systems and machines used to produce hydropower, the processes of setting up such systems, and their associated costs and environmental impacts.