This chapter focuses on the plasticity now known to be possible in the motor regions of the brain. It explores the recent findings regarding motor cortex plasticity and reorganization. The most common approach taken to investigate the potential for cortical plasticity has been to evaluate the reorganization of sensory and motor maps following peripheral or central lesions and compare them to normal animals. The chapter also explores the structure of the motor cortex and how it relates to plasticity. The motor cortex contains a neural circuitry conducive to motor plasticity, which includes both intrinsic and extrinsic components. The chapter presents an overview of the development in a new field of rehabilitation, neural prostheses, also called brain-machine interfaces (BMIs). Neural prostheses open an important window into plasticity by allowing detailed research into how the brain changes with practice and learning and the extent to which the brain is able to adapt.