This book describes methods for interfacing with the neuromuscular system in order to control external devices, with the goal of motor rehabilitation. It provides overviews of main topics relevant for establishing interfaces between the body and external systems, such as electrodes and signal processing, as well as more detailed information on some applications, such as brain-computer interfaces. Readers new to these topics will find this an understandable presentation of the field. Senior-level researchers will also find the book useful, especially for the parts related to the most advanced topics.