Music therapy is the use of interventions to accomplish individual goals within a therapeutic relationship by a professional who has completed an approved music therapy program. Music therapy is an allied health profession and one of the expressive therapies, consisting of a process in which a music therapist uses music and all of its facets—physical, emotional, mental, social, aesthetic, and spiritual—to help clients improve their physical and mental health. Music therapists primarily help clients improve their health in several domains, such as cognitive functioning, motor skills, emotional development, social skills, and quality of life, by using music experiences such as free improvisation, singing, and listening to, discussing, and moving to music to achieve treatment goals. It has a wide qualitative and quantitative research literature base and incorporates clinical therapy, psychotherapy, biomusicology, musical acoustics, music theory, psychoacoustics, embodied music cognition, aesthetics of music, sensory integration, and comparative musicology. Referrals to music therapy services may be made by other health care professionals such as physicians, psychologists, physical therapists, and occupational therapists. Clients can also choose to pursue music therapy services without a referral (i.e., self-referral).