Opus number
Opus is a Latin word which means "work" (in the sense of "a work of art").
Some composers' musical pieces are identified by opus numbers which generally run either in order of composition or in order of publication. The usual abbreviation is "Op.". "WoO" stands for "Werk ohne Opus" or "work without an opus number" (particularly in the music of Beethoven). "Op. posth." means "opus posthumous" or "work [published] posthumously".
Certain composers' works, particularly from the baroque and classicist era, when works were less often written specifically for publication, and when publication numbers that do exist are both inconsistent or unhelpful (two opus 1 sets of violin sonatas for Mozart, for instance), have been definitively cataloged by a given scholar, and in such instances these works can be unambiguously referred to by their thematic catalog abbreviations.
- Johann Sebastian Bach works are referred to by their BWV or Bach Werke Verzeichnis numbers after the catalogue by Wolfgang Schmieder.
- Marc Antoine Charpentier's works are referred to by the H or Hitchcock numbers after Hugh Wiley Hitchcock.
- Joseph Haydn's works are referred to by their Hob or Hoboken numbers after Anthony van Hoboken's 1957 classification.
- Franz Liszt's works are referred to by their S or Searle numbers after Humphrey Searle's 1960s classification The Music of Liszt. Alternately, R is used to refer to Peter Raabe's 1931 reference Franz Liszt: Leben und Schaffen.
- Wolfgang Amadeus Mozart works are referred to by their K or Köchel numbers, after Ludwig von Köchel. In continental Europe, the German acronym "KV" for Köchel Verzeichnis is more common. See also: List of compositions by Mozart
- Franz Schubert works are referred to by their D or Deutsch numbers after Otto Erich Deutsch's catalogue.
- Antonio Vivaldi works are referred to by their RV or Ryom Verzeichnis numbers after Peter Ryom's catalogue.
- Richard Wagner works are referred to by their WWV or Wagner Werke Verzeichnis, which also include his non-musical work.
- Two numberings systems are extant for the harpsichord works of Domenico Scarlatti: the L or Longo numbers after Alessandro Longo's edition for piano, and the K or Kirkpatrick numbers after Ralph Kirkpatrick's facsimile edition.