The third edition of this book is the culmination of a 25 year project aimed at conceptualizing music therapy in a critically inclusive and integrative way. To be critically inclusive, the definition must provide an umbrella that embraces all professional practices and concepts that have been deemed viable in the refereed literature, while also excluding those concepts and practices: that do not rely on music; that occur outside of a professional therapist-client relationship; and that are not concerned with addressing the client’s health. To be integrative, the definition must offer myriad options for using music to address the client’s health concerns—as indicated by client need rather than therapist orientation.The resulting definition is a working and provisional one, based on over 100 existing definitions. It has been co-constructed by the author (who is situated in American music therapy), experienced colleagues, and authors and associations around the world who have crafted their own definition of music therapy. Its relevance is clearly situated with Western cultures that use the English language for scholarly purposes.