Books, periodicals, and printed music are arranged on the shelves according to the Library of Congress Classification system. If you know the system, you can browse the shelves efficiently and use the online catalog to see what the library has in a particular classification by doing a call number search.
In the Library of Congress Classification system class numbers begin with one, two or three letters followed by a whole number. Music is organized by the kind of material: so all the piano sonatas are in one place and all the string quartets in another. Call numbers for music materials all begin with the letter M. The following is a brief outline of the call numbers for music: for a detailed list see M: Music and Books on Music, Library of Congress Classification.
See a listing of the library's 20th century music holdings by using the following LC class/subject correlations.