Für Elise
Beethoven's works are classified by both genre and various numbering systems. The best-known numbering system for Beethoven's works is that by opus number, assigned by Beethoven's publishers during his lifetime. Only 172 of Beethoven's works have opus numbers, divided among 138 opus numbers. Many works that were unpublished or else published without opus numbers have been assigned either "WoO" ("Werke ohne Opuszahl"—works without opus number), Hess or Biamonti numbers. For example, the short piano piece "Für Elise", is more fully known as the "Bagatelle in A minor, WoO 59 ('Für Elise')". Some works are also commonly referred to by their nicknames, such as the "Kreutzer" Violin Sonata, or the "Archduke" Piano Trio.