This book describes a fascinating aspect of the brain and the spinal cord, namely that the brain is malleable which means that the way it works can be changed. Something changes in the brain whenever we learn something, but changes also happens when training to reach new skills. Rehabilitation after strokes and trauma is successful because it brings on changes in the way the brain functions. It is the brain's ability to change its functions that makes it possible to use prostheses of different kinds such as cochlea implants that can make deaf people hear. The young brain is more malleable than it is later in life. It also discusses these two very different roles of neural plasticity, one that is beneficial and one that causes harm and diseases; it discusses the sparse knowledge about the role of neural plasticity in other disorders and it speculate that neural plasticity may be involved in addictions of various kinds and in diseases such as depression.