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Adjustable-speed electric motor/generator drives (ASDs) are used to save electric energy and increase productivity in variable-output work processes of all new and well-established industries such as: digital information gadgets, digital home appliances, automotive and robotics electric actuators, pump compressors, other vehicles, industrial processes, and distributed and renewable energy system electric generators. With power levels that go from less than 1 W to hundreds of megawatts, ASDs have become in the last 20 years a very dynamic worldwide industry/market. The recent advances in electric/magnetic materials, modeling tools, design and fabrication of electric machines for ASDs, corroborated with matched progress in ASD power electronics with power quality control, DSP menu based control, novel sensors and interfacing, field orientation and direct torque control (FOC and DTC), and advanced state observers for motion or current sensorless control, has prompted us to do this selective review. This article selects a few control issues in ASD, such as performance indices, three-phase ac motor control principles, wide constant power speed control, motion-sensorless control of ac drives, variable-speed ac generator control, and linear motor drives control, and discusses their basics, recent progress, and a few directions of ASD research and industrial development for the near future.