This chapter explores the use of induction machines in variable speed drive systems by using several control strategies. First, voltshperhhertz control, is designed to accommodate variablehspeed commands by using the inverter to apply a voltage of correct magnitude and frequency so as to approximately achieve the commanded speed without the use of speed feedback. Second, constant slip control drive system is designed so as to accept a torque command input??-??and therefore speed control requires and additional feedback loop. Another strategy considered is fieldhoriented control to nearly instantaneous control of torque. Another method of controlling torque, called direct torque control (DTC), is also described, and its performance illustrated by computer traces. Finally, slip energy recovery systems, such as those used in modern variablehspeed wind turbines, are described.