This chapter describes the types of cooling tower design and discusses the various techniques of load-following capacity controls. The optimization strategies are not limited to standard cooling towers but also include the evaporative types and the free cooling configurations. The chapter covers cooling tower winterizing and blowdown controls. In a cooling tower, heat and mass transfer processes combine to cool the water. The mass transfer due to evaporation does consume water, but the amount of loss is only about 5% of the water requirements for equivalent once-through cooling by river water. If the temperature of the water supplied by the cooling tower is controlled by modulating the fans, a change in the cooling load will result in a change of the operating level of the fans. The cooling tower water temperature must always be lower than the desired process temperature on the other side of the process heat exchangers.