The Field Orientation Principle (FOP) constitutes a fundamental concept behind the modern technology of high-performance, vector-controlled drive systems with AC motors. The recent interest in these systems has been spawned by the widespread transition from DC to AC drives in industry. Induction motors, industry's traditional workhorses, are particularly well suited for FOP-based vector control. This text presents the FOP in a simple, easy-to-understand framework based on the space-vector dynamic model of the induction machine. Relationships between the classic phasor equivalent circuits of the motor and their vector counterparts are highlighted. A step-by-step derivation of dynamic equations of the motor provides a formal background for explanation of the basic approaches to vector control. In addition, the author presents scalar control methods for low-performance drives as an intermediate stage between uncontrolled and high-performance drives. The reader will also find a full chapter devoted to power inverters, which constitute an important component of adjustable speed AC drive systems, and a review of associated issues such as observers of motor variables, parameter estimation, adaptive tuning, and principles of the position and speed control of field-oriented induction motors. Numerical examples and computer simulations illustrate the ideas and techniques discussed. This text is a practical resource and should be a useful for researchers and students interested in motor control, power and industrial electronics, and control theory.