Robotic rehabilitation devices have become increasingly important and popular in clinical and rehabilitation environments to facilitate prolonged duration of training, increase the number of repetitions of movements, improve patient safety, decrease the strain on therapists, and eventually, to improve the therapeutic outcome. Novel assistive technologies are becoming available as wearable devices that allow transferring the therapeutic training into home and work environments or assist the patient in daily life activities. Rehabilitation Robotics summarizes the rationale for robot-assisted therapy and presents the technological steps in the evolution of the design and development of lower and upper extremity rehabilitation robots. After presenting the basic mechanisms of natural and artificial movement restoration, and the rationale for robot-aided movement therapy, it outlines several design criteria that are relevant for the development of effective and safe rehabilitation robots. Rehabilitation Robotics also includes a short overview of existing clinical trials that have been performed showing that the application of rehabilitation devices is at least as effective as the application of conventional therapies. It concludes with the finding that further clinical studies are required to find predictors for the success of a robot-aided treatment. Rehabilitation Robotics is an ideal primer for anyone with a research or professional interest in robotic devices that provide technical support to the impaired human motor system.