We describe general concepts about motor imagery and differences to motor execution. The problem of controlling what the subject actually does during imagery is emphasized. A major part of the chapter is dealing with mental training by imagery and the usage of motor imagination in athletes, musicians and during rehabilitation. Data of altered representations of the body after loss of afferent information and motor representation due to limb amputation or complete spinal cord injury are demonstrated and discussed. Finally we provide an outlook on additional work about motor imagery important for further understanding of the topic.