Feedback control has always been an essential part of jet engines because they operate at or near their mechanical or aerothermal limitations. In this paper, the basics of controlling an engine while satisfying numerous constraints will be reviewed. The emphasis will be on commercial engines though most of the material is also applicable to military engines. In the first part, a simplified theory of engine operation is discussed in terms of the basic principles and limitations for each component. The second part of the paper discusses overall control requirements and typical sensors and actuators. Finally various control strategies are presented. It is shown that much of the complexity of the control comes from the need to operate the engine as close as possible to its limits. In a commercial engine, this results in a series of single input single output controllers. The case for multivariable control can be more strongly made for military engines especially those with additional flowpath geometry actuators such as a variable cycle or advanced short takeoff and landing engines.