The regenerative liquid ring (RLR) pump is a type of rotodynamic machine which has the ability to develop high heads at relatively low flow rates in only one impeller stage. Although the exact principle of operation of this type of pump has been a phenomenon not fully understood, it has nevertheless been widely applied for over a century in areas of liquid pumping. Despite the low efficiency, RLR pumps have several advantages over other turbomachines with similar tip speed due to relatively low manufacturing costs, simplicity, high reliability, enhanced priming behaviour and can in many applications offer a more efficient alternative. Efficiency improvements are key to reducing energy consumption and ultimately combatting the global climate change. This paper offers an extensive review into the development, performance challenges and design improvements of RLR pumps in order to provide some useful insight on future research and next steps, with a particular focus on improving efficiency throughout the pump life cycle.