It looks like you're using Internet Explorer 11 or older. This website works best with modern browsers such as the latest versions of Chrome, Firefox, Safari, and Edge. If you continue with this browser, you may see unexpected results.
"The Library of Congress Classification (LCC) is a classification system that was first developed in the late nineteenth and early twentieth centuries to organize and arrange the book collections of the Library of Congress."
-- https://www.loc.gov/catdir/cpso/lcc.html
Library of Congress Classification
The music book collection is arranged by Library of Congress classification. The books are organized into three groups, the main class M and the two subclasses, ML and MT.
M - Music
ML - Literature on music
MT - Instruction and study
More About LoC Classification
In the Library of Congress Classification system, all knowledge is divided into 21 classes, each identified by a single letter of the alphabet (e.g. M for Music). Read more about the LoC Classification system here: http://www.loc.gov/catdir/cpso/lcc.html
Example of a Music Book Call Number
Book:
12 bass arias from the cantatas: an album of flute duets, by Johann Sebastian Bach. Kentfield, CA: Raymond A. Ojeda, 1986.
Call Number:
M289
.B28 C26 1986
- refers to the subject, arranged music for wind instruments