In music, the BACH motif is the sequence of notes B flat, A, C, B natural.

This four-note motif has been used by a number of composers, usually as a homage to Johann Sebastian Bach. The first known example, however, is in a piece by Jan Pieterszoon Sweelinck—it is possible, though not certain, that he used it in homage to one of Johann Sebastian's ancestors, many of whom were themselves musicians.

The possibility of being able to spell the surname Bach in this way comes about because in German B indicates what in English is called B flat, while H indicates what in English is called B natural.

J. S. Bach himself used it as a fugue subject in the final part of Die Kunst der Fuge (BWV 1080), a work he did not complete before he died in 1750. It appears in passing in several of his other pieces, such as at the end of the fourth of the canonic variations on "Vom Himmel Hoch", BWV 769. Its appearance in the penultimate bar of the Kleines harmonisches Labyrinth, BWV 591, is not thought to be very significant and the work may even be spurious (Johann David Heinichen has been suggested as a possible composer). It shows up in the St Matthew Passion in the section where the chorus sings "This man was God's own son most truly." In many pieces, while the exact notes B-A-C-H are not played, a transposition of the motif is used (a note sequence with the same intervals: down a semitone, up a minor third, down a semitone).

A fugue for keyboard in F major by one of Bach's sons, probably either Johann Christian Bach or Carl Philipp Emanuel Bach, exists using the motif, but it was not until the 19th century when interest in Bach was revived that the motif began to be used with any regularity.

Perhaps because it was used by Bach himself in a fugue, the motif is often used by other composers in fugues or other complex contrapuntal writing.

Works which prominently feature the BACH motif include, in chronological order:

• Robert Schumann - Six Fugues for organ, pedal piano or harmonium, opus 60 (1845)
• Franz Liszt - Fantasie und Fuge über das Thema B-A-C-H, for organ (1855, later arranged for piano)
• Max Reger - Fantasia and Fugue on B-A-C-H for organ (1900)
• Ferruccio Busoni - Fantasia contrappuntistica for piano (first version 1910, later versions 1912 and 1922)
• Arthur Honegger - Prélude, Arioso, Fughette for piano (1932, later arranged for string orchestra)
• Francis Poulenc - Valse-improvisation sur le nom Bach for piano (1932)
• Anton Webern - String Quartet (1937-38) - the tone row is based on the BACH motif
• Jean Coulthard - Variations on BACH for piano (1952)
• Luigi Dallapiccola - Quaderno musicale di Annalibera (1952)
• Arvo Pärt - Collage over B-A-C-H for strings, oboe, harpsichord and piano (1964)
• Milos Sokola - Passacaglia quasi Toccata on B-A-C-H for organ (1976)
• Alfred Schnittke - Concerto Grosso No. 3 (1985)
• Ron Nelson - Passacaglia (Homage on B-A-C-H) for wind ensemble (1990s)

The motif features in passing in a number of other works including Arnold Schoenberg's Variations for Orchestra (1926-28) and his String Quartet No. 3 (1927), Krzysztof Penderecki's St Luke Passion, and Johannes Brahms' cadenza for the first movement of Ludwig van Beethoven's Piano Concerto No. 4.

Other signature motifs include:

• F, E flat, C, B natural for Franz Schubert (F. Schubert)
• E flat, C, B natural, B flat, E, G for Arnold Schoenberg (Schönberg)
• D, E flat, C, B natural for Dmitri Shostakovich (D. Schostakowitsch)

These are possible because the German for E flat is "Es".

• B, E, B, A or B, A, B, E for Béla Bartók (Béla Bartók, the latter motif recognizing the Hungarian practice of placing the family name before the personal name)
• C, A, G, E for John Cage, used by Pauline Oliveros[1]
• A, B flat, B natural, F for Alban Berg and Hanna Fuchs-Robettin (A. B. and H. F.), used in Berg's Lyric Suite