A few of the Music Library's most important holdings are shelved across the street, at the Beinecke Rare Book and Manuscript Library. You can recognize them in Orbis because the Location is "BEINECKE, Music Library Deposit" and the Call Number is "Music Deposit" followed by a number.
In addition to the Music Library materials shelved there, the Beinecke Library has very rich musical holdings of its own, ranging from the 15th-century Mellon Chansonnier to a manuscript of Mahler's Symphony No. 1 that includes a movement that the composer later decided to omit. They are listed in Orbis or the Yale Finding Aid Database.You can also read about some of the highlights in an essay, Music in the Beinecke.
To study any of these items, please consult the Beinecke Library directly.