Werke ohne Opuszahl ("Works without opus number") (WoO) is a German musical catalogue prepared in 1955 by Hans Halm and Georg Kinsky, listing all of the compositions of Ludwig van Beethoven that were not originally published with an opus number, or survived only as fragments.
- Dahlhaus, Carl (1991). Ludwig Van Beethoven: Approaches to His Music. Oxford University Press. p. 241. ISBN 0198163991.
- Yale University. "Thematic catalogs". Yale University Library. Retrieved 11 July 2013.
- Université du Québec. "Identification des catalogues thématiques d'oeuvres". Université du Québec.ca. Retrieved 11 July 2013.
- Raff.org. "Catalogue: WoO (Works without Opus Numbers)". Raff.org. Retrieved 11 July 2013.