The potential advantages of variable-speed hydroelectric generation are discussed in this article. Some general aspects concerning the efficiency gains in turbines and the improvements in plant operation are analyzed. The main results of measurements on a test loop with an axial-flow turbine are reported. Also, we describe the control scheme implemented, which is based on artificial neural networks. To confirm the practical interest of this technology, the operation of a run-of-the-river small hydro plant has been simulated for several years. Substantial increases in production with respect a fixed-speed plant have been found.