"Musical source" is a broad term with several different meanings. In Library of Congress Classification, musical sources are the volumes classified in M2 through M2.3 which consist of various monuments and facsimile series. Oxford Music Online defines a monument as a "multi-volume series in which the majority of individual volumes present a unified musical repertory derived from the same or from closely related original sources." In other words, unlike a complete edition which focuses on a single composer, a monument selects works by several composers, named or anonymous, in an attempt to draw connections between them or illustrate a common theme. While monuments are often thoroughly-annotated scholarly editions, other series are facsimiles which are copied more-or-less precisely from an unedited original.
The designation "musical source" can also refer, more generally, to any music or writing on music which has come to us direct from its creators whether or not it is classified in M2. Especially in the internet age, we have the ability to view digitized reproductions of rare handwritten manuscripts and early printed editions preserved in libraries, archives, and other collections around the world from the convenience of a personal computer, tablet, or smartphone. This development has challenged the notion of the conventional print facsimile: aging, black-and-white paper copies of these sources are no longer required, nor even desirable, when the original itself can be viewed in a high resolution, color image. Nevertheless not everything has been digitized, and there is much more to M2 than only facsimiles.
See the lists below for musical sources held in the Music Collection as well as, in the final box, several online locations for digitized manuscripts. For more information on musical sources, refer to the entries for "Editions, historical" and "Sources, MS" at Oxford Music Online.
Browse the list below for titles of some of the major musical sources held in the print Music Collection. Hover over the info icon to see the call number and a brief description of the series or volume, and follow the link for more information on its contents. Notice especially series identified as Recent Researches in Music, several long-running and prestigious series issued by A-R Editions, or those published by Garland. The German word Denkmäler, meaning "monument" or "memorial," appears in several titles as does the Latin, Monumenta. Others like Le Trésor des pianistes and The Wa-Wan Press are of special historical significance.
Range #1: Analytic Symphony to Recent Researches
Range #2: Recent Researches to Women Composers
Range #15: Oversize -- Elías to Le Roman de Fauvel
The vast majority of musical sources are classified in M2. There are, however, several additional sources in M2.3 where they are separated by region or country as indicated by their first cutters (i.e., U6 = United States). These can be found in Range #2 immediately following the M2s. There are no oversize or miniscores for M2.3.
Although not strictly musical sources, there are several related titles and series classified in M1 miscellaneous collections. Most are shelved in Range #1 immediately preceding the M2s while a few oversize volumes are in Range #15.