What are Opus Numbers?

Beethoven's compositions by Opus numbers


Opus numbers indicate the chronological order of publication of Beethoven's compositions.    

In most cases, every individual work has its on opus number (e.g. each of the nine symphonies has its own opus number).  But often several works are grouped together under one opus number.  This began Beethoven's first publication, Opus 1 in 1795, which included his first three piano trios (Piano Trio No. 1, Piano Trio No. 2, Piano Trio No. 3).   

Generally, the order of publication is in alignment with the order of the composition of the pieces, at least within a year or two.  But often composition were published years after they were written.  For instance, Piano Sonatas No. 19 and No. 20 were published as Opus 49 in 1805, but were written in the late 1790s before Piano Sonata No. 8, Opus 13 ("Pathetique") from 1799.  Had they been published when they were written they would have had much lower sonata and opus numbers.

Finally, compositions that were never published are distinguished in several ways, most commonly as "WoO" numbers (Without Opus).

Beethoven's most famous WoO composition is WoO 59, Bagatelle No. 25 in A minor, commonly known as "Für Elise" which was written around 1810 but never published.