Sometimes the challenge in locating a piece of music lies in verifying the facts. Some pieces have opus numbers, other numbering (e.g., Quartet No. 2), key designations (e.g., E-flat major), or even nicknames (e.g., the American Quartet). Knowing this information can help you in locating this piece in the Library. The two major types of tools to use for verifying this type of information are 1) the New Grove Dicitionary of Music and Musicians works lists and, 2) the composer's thematic catalog.
Most composers listed in the New Grove Dictionary of Music and Musicians (print Ready Reference ML100 G76N38 2001 and online in Grove Music Online via Oxford Music Online) have a detailed works list at the end of their entry. Information includes opus and other numbering, title(s), key designations, date of composition. Sometimes it also includes date of publication, instrumentation, premiere information, and collected works locator information.
If Grove does not have the information you need, you may need to use a thematic catalog for that composer (see below).
Thematic catalogues provide lists of composer's works in an organized fashion; many include incipits for the beginning of each work/movement. Often this is by opus number or chronology. Well-known examples are Otto Deutsch's Schubert thematic catalogue and Bach's BWV Bach Werke‐Verzeichnis (Index to Bach's Works). For a more detailed definition, see the entry in Grove. Thematic catalogs can also help you locate individual works in a composer's collected edition.
To find a thematic catalogue for a particular composer you can:
To find a thematic catalogue for a composer using Grove Online, search for the composer and then select "Works" under the the Article Contents on the left. Thematic catalogues for that composer will be listed before the works list and after editions.