Music therapy is being acknowledged as one of the therapies that have been proven valuable in helping children with developmental delay to enhance communication. The theoretical foundations of the use of music therapy can be found in developmental psychology. This book presents a study done with a child with fragile X syndrome during the course of music therapy. It focuses on the role of the child ́s favorite instrument in enhancing communication and relates this role to the concept of intermediary object. It offers an overview of the theoretical foundations of music therapy and its use with developmentally delayed children. It also presents the different definitions of intermediary object that appear in the music therapy literature as well as the origin of this concept in the field of psychodrama. The text presents a unified view of the relationship between the use of music therapy and the theories that lie behind it. The book is intended to help parents or professionals that are working with children with fragile X syndrome or other neurodevelopmental disorders.