Performing editions: These are the scores that you'll find on the 2nd floor of MPAL. They have been edited by publishers and teachers/performers to include fingerings, phrasing, and sometimes tempo indications. These editions range in quality, but you'll find that publishers such as Henle, Wiener Urtext, Breitkopf and Hartel (among others) tend to put out better editions than, for example, International.
Collected editions/critical editions: These are sets of composers' collected works. They have been compiled by scholarly editors to try to give the closest indication of what the composer truly intended. Critical commentary is included that discusses any alterations in accidentals, notes, ornaments, and so forth. The editors refer to any manuscript sources available and also research whether the composer later made changes (such as notes or cuts, etc.). These editions are also sometimes called ‘complete editions’ or ‘Gesamtausgabe’.
Monuments or Denkmäler: Are collected editions that focus on a particular country, region, or type of music rather than a single composer.
See "Editions, historical." article in Oxford Music Online for a more complete definition. For common abbreviations of larger Denkmäler (e.g., DTO is Denkmäler der Tonkunst in Ö̈sterreich) see the abbreviations list in Grove (Oxford Music Online > Tools & Resources > Abbreviations and Library Sigla > Bibliographical Abbreviations).
To locate individual items in a collected works set using Grove in Oxford Music Online (linked below), search for the composer and then select "Works" under the the Article Contents on the left.
Collected editions for that composer will be listed at the start of this section. Note the abbreviation in brackets at the end of each listing.
Find the piece you are looking for in the works list. The right-hand columns will tell you where in the composer's collected works you can find that piece.
It can also be useful to refer to the following print resources to identify a collected edition:
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.