The use of reverse-running pumps as turbines (PATs) is a promising technology for small-scale hydropower. This thesis reviews the published knowledge about PATs and deals with some areas of uncertainty that have hampered their dissemination, especially in 'developing' countries. Two options for accommodating seasonal flow variations using PATs are examined and compared with using conventional turbines (that have flow control devices). This has been done using financial parameters, and it is shown' that, under typical conditions, PATs are more economic. The various published techniques for predicting the turbine-mode performance of a pump without expensive tests are reviewed; a new heuristic one is developed, and it is shown (using the same financial parameters and a large set of test data in both modes of operation) that the cost of prediction inaccuracy is negligible under typical circumstances. The economics of different ways of accommodating water-hammer are explored. Finally, the results of laboratory tests on a PAT are presented, including cavitation tests, and for the latter a theoretical framework is exposed.