Opus (from the Latin for “work”) is a numbering system that took shape in the 17th century. The composer or their publisher numbers works in order of creation or publication.
“Op. 1” is usually the composer's debut, while the last opuses are the summation of a path. Beethoven's Op. 131 (String Quartet in C-sharp minor) is a late-period masterpiece, completed in 1826, months before his death. For some composers, musicologists maintain the catalog: Bach — BWV (Bach-Werke-Verzeichnis), Mozart — K (Köchel-Verzeichnis), Schubert — D (Deutsch). This is the universal language of academic music, letting us pinpoint any work in the world repertoire.
