Among the Music Library's holdings of rare materials are first and early editions of treatises, libretti, and printed music as well as facsimiles of manuscripts and other primary sources. Rare books and scores can be located via NUsearch. 
Over 1,300 music manuscripts and nearly 1,000 pieces of correspondence comprise the General Manuscript Collection. Although this collection represents music from the 14th century to the present, emphasis in placed in four areas:
Most materials in the General Manuscript Collection can be located in NUsearch  and WorldCat. Records will contain detailed bibliographic information and a link to a digital image of each item. Such images are intended for educational purposes and to assist researchers in the identification of particular works or sources.
The Music Library is home to archival collections that document the work of particular composers, conductors, performers, and organizations through manuscripts, correspondence, and other primary sources. Collections relating to experimental music since 1945 include the archives of John Cage, Ben Johnston, Robert Moran, and the ONCE group, while further holdings, such as the Fritz Reiner Library, the Ricordi Collection, and a portion of the Moldenhauer Archives, represent other important musicians, styles, and eras. Archival collections held by the Music Library include:
Music Library special-collections materials are available to Northwestern University students, faculty, and visiting researchers for on-site examination by appointment only and in accordance with the Policy for Using Rare Music Library Materials . Unprocessed collections are accessible only under special circumstances. Inquiries regarding access to or reproduction of Music Library special-collections materials should be directed to the Head of the Music Library .