Werke ohne Opuszahl (Works without opus number), abbreviated WoO, is a German musical catalog prepared by Hans Halm and Georg Kinsky in 1955. The goal was to list all Beethoven compositions that were not numbered with opus numbers or exist only in fragments. The original German title was Das Werk Beethovens: Thematisch-bibliographisches Verzeichnis seiner sämtlichen vollendeten Kompositionen.
Example for WoO numbering: Beethoven – Allegretto for Piano Trio, WoO 39
The WoO numbering is also used for other composers’ works, such as Schumann, Brahms or Clementi.
