The Bach-Werke-Verzeichnis (Bach Works Catalogue) is the numbering system identifying compositions by Johann Sebastian Bach. The prefix BWV, followed by the work's number, is the shorthand identification for Bach's compositions. The works are grouped thematically, not chronologically.
Wolfgang Schmieder assigned the BWV numbers in 1950, to indicate the work's placement in the Bach works catalogue titled Thematisch-systematisches Verzeichnis der musikalischen Werke von Johann Sebastian Bach (Thematic-Systematic Catalogue of Musical Works of Johann Sebastian Bach). For example, the Mass in B minor is BWV 232. Works believed incomplete or of doubtful authenticity at the time of cataloguing were listed in the BWV Anhang (BWV Appendix), and are identified by BWV Anh number. The BWV catalogue is occasionally updated, with newly discovered works added at its end, though spurious works do not have their numbers removed.
The BWV numbers are universally used and accepted as the standard numbering of Bach's works. Some older publications refer to the BWV numbers as Schmieder numbers and designate them with the prefix S rather than BWV (for example, writing S. 232 instead of BWV 232).