Rotating biological contactors (RBCs) offer an alternative treatment technology to the conventional activated sludge process. The principal advantages of the RBC stem from the fact that the interfacial area generated is very high and practically independent of the speed of rotation, unlike in the activated sludge process. In the present work, the process design aspects of RBCs are reviewed. The published literature on various aspects such as media employed in RBCs, hydrodynamic characteristics, power consumption, and mass-transfer characteristics is reviewed. The various models proposed for the design of RBC systems are reviewed. A stepwise procedure is given for the process design of an RBC system. The RBC system is compared with the other wastewater treatment facilities such as the activated sludge process and trickling filters in terms of its oxygen-transfer efficiency.