The New Grove Dictionary of Music and Musicians is an encyclopedic dictionary of music and musicians. Along with the German-language Die Musik in Geschichte und Gegenwart, it is one of the largest reference works on the history and theory of music. Earlier editions were published under the titles A Dictionary of Music and Musicians, and Grove's Dictionary of Music and Musicians; the work has gone through several editions since the 19th century and is widely used. In recent years it has been made available as an electronic resource called Grove Music Online, which is now an important part of Oxford Music Online.

Music theory is the study of the practices and possibilities of music. The Oxford Companion to Music describes three interrelated uses of the term "music theory": The first is the "rudiments", that are needed to understand music notation ; the second is learning scholars' views on music from antiquity to the present; the third is a sub-topic of musicology that "seeks to define processes and general principles in music". The musicological approach to theory differs from music analysis "in that it takes as its starting-point not the individual work or performance but the fundamental materials from which it is built."