Köchel number

The Köchel-Verzeichnis or Köchelverzeichnis is a chronological catalogue of compositions by Wolfgang Amadeus Mozart, originally created by Ludwig von Köchel, in which the entries are abbreviated K. and KV. The numbers of the Köchel catalogue reflect the continuing establishment of a complete chronology of Mozart's works, and provide a shorthand reference to the compositions.

According to Köchel's counting, Requiem in D minor is the 626th piece Mozart composed, thus is designated either K. 626 or KV 626; however, his original catalogue (1862) of Mozart has been twice revised, and some works have had three KV. numbers, e.g. Mozart's Horn Concerto No. 1, K. (412+514)/386b.

In the decades after Mozart's death there were several attempts to catalogue his compositions, for example by Franz Gleißner and Johann Anton André (published in 1833), but it was not until 1862 that Ludwig von Köchel succeeded in producing a comprehensive one. Köchel's 551-page catalogue was titled Chronologisch-thematisches Verzeichnis sämmtlicher Tonwerke W. A. Mozarts (Chronological-thematic Catalogue of the Complete Musical Works of W. A. Mozart). Köchel attempted to arrange the works in chronological order, but many compositions written before 1784 could only be estimated, although Leopold Mozart had compiled a partial list of his son's earlier works; Mozart's catalogue of his own compositions (begun in February 1784 with K. 449) allows relatively precise dating of many of his later works. The catalogue included the opening bars of each piece, known as an incipit. Köchel divided the corpus into a main chronology of 626 works, and five appendices ( in German, abbreviated to Anh.) The appendices (Anh. I-V) included:

Since Köchel published his original catalogue in 1863 (now referred to as K¹), the dating of Mozart's compositions has been subject to constant revision. Many more pieces have since been found, re-dated, re-attributed and re-numbered, requiring three revised editions of the catalogue. Subsequent editions - especially the third edition (K³) by Alfred Einstein (1937), and the sixth edition (K⁶) by Franz Giegling, , and Alexander Weinmann (1964) - have reflected attempts to arrange the growing list of works in a more accurate chronological order, according to various levels of scholarship.

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