Electric power generation is one of the most relevant issues in recent decades. This energy can be obtained through non-renewable sources, renewable sources, and especially non-conventional renewable sources. Within this last category, we can classify the use of a Pump as a turbine (PAT). The pumps are hydraulic machines designed for energy expenditure. Thanks to being reversible machines, PATs can be used in their reverse mode of operation to extract valuable energy from the fluid. However, this use can generate some inconveniences in its process, ranging from assembly, characterization, and hydrodynamic phenomena. This article provides the basic theoretical concepts and operating curves typically used for pumps as turbines. In addition to a global approach to the hydrodynamic phenomena associated with using pumps as turbines, there are cases of vibration, cavitation, and rotating stalls. All this panorama is complemented with some examples of application and economic analysis that ratify the advantages of using pumps as turbines as a reliable source of energy generation.