During his life, Wolfgang Amadeus Mozart
wrote hundreds of pieces of music, selling as many of them as possible to private interests such
and wealthy commoner
s. These works, once sold, disappeared into the buyer's private collection
and out of the public's view. Mozart kept poor records of these pieces, considering them akin to pot boiler
s, composed and sold to support his family and himself. When he died in 1791, Mozart left behind only these insubstantial records, along with multiple unfinished
works without titles or dates. Accordingly, his catalog was a mess -- even though interest in his work rose greatly in the sixty years after his death, there
about how many pieces he had composed and when he had composed them, and indeed whether he should even receive credit for certain others.
While sub-catalogs were compiled by interested parties -- Joseph Haydn among them -- in that time, a complete catalog was never attempted. Around 1850, a botanist named Ludwig Alois Friedrich von Köchel decided to change that. In 1862 Chronologisch-thematisches Verzeichnis samtlicher Tonwerke Wolfgang Amadé Mozarts (Chronological-Thematic Catalog of the Complete Works of Wolfgang Amadeus Mozart) was finally published, and covered all 626 (!) of Mozart's known compositions, in rough chronological order.
Since then there have been six revisions of the catalog, and it has become the global standard system to reference Mozart's work. The last edition was published in 1964, and edited by historians Franz Giegling, Alexander Weinmann and Gerd Sievers. Notably, it contains sub-entries for fragments and unfinished pieces that share structure with finished ones, whereas Köchel's edition largely ignored these fragments. Also, some pieces incorrectly attributed to Mozart in the original catalog were removed, and pieces discovered since then were
References to Köchel numbers usually take the form K 256 where 256 is the sixth-edition number referring to Aria for Tenor,
"Clarice cara mia sposa", and so forth. Occasionally the notation might look like K 454a (460), where 454a is the sixth-edition
entry and 460 is the first-edition entry. Sometimes KV is substituted for K, where the V signifies Verzeichnis, German for catalog.