Great Fantasia and Fugue in G minor, BWV 542

The Great Fantasia and Fugue in G minor, BWV 542, is an organ prelude and fugue by Johann Sebastian Bach. It acquired that name to distinguish it from the earlier Little Fugue in G minor, which is shorter. This piece is not to be confused with the Prelude and Fugue in A minor, which is also for organ and also sometimes called "the Great".

It was transcribed for piano by Franz Liszt as S.463. Modern arrangers have orchestrated the work.

According to musicologist Christoph Wolff, Bach in 1720 performed the organ fugue on occasion of his visit to Johann Adam Reincken at Hamburg, the theme of which is based on a Dutch popular tune (called 'Ik ben gegroet van…'), presumably as an homage to Reincken's Dutch origin.