This chapter describes the automatic control of fans and describes strategies for minimizing their costs of operation. Fans are classified into axial flow and radial flow types according to the nature of the flow through the blade passages. Tubeaxial and vaneaxial fans are made with adjustable pitch blades in order to permit the balancing of the fan against the system or to make infrequent adjustments. The fan station is optimized when it is meeting the process demand for air or other gases at the lowest possible cost. The fan cycling control described can be used to cycle any number of parallel fans. The minimum cost of operation is achieved by first minimizing the number of fans in operation and then minimizing the power consumption of the operating fans. All fans must always operate to the right of the surge point.