In this study, several aspects of music therapy are presented, concerning the diagnosis and assessment of Autism Spectrum Disorder, as well as the treatment intervention. Beginning from the definition of music therapy, it is highly noticed that there is no globally accepted definition. However, the definition of the American Music Therapy Association (ΑΜΤΑ) is frequently used and is considered to be the best of all. A brief reference to the beginning, the goals and the theories of music therapy is presented. Additionally, using music therapy as tool for diagnosis, the contribution of music in the therapeutic process and the importance of the relationship between the music therapist and the child are analysed. Finally, certain negative aspects of music therapy are referred. In conclusion, this study targets to inform special education teachers about music therapy and its several aspects, including a review of recent studies.