Composed in 1782, published in 1800. Although the prelude is often published as a “Fantasia,” Mozart himself referred to it as a “Prelude.” The fugue was composed first, and the prelude was then composed “to precede it.” Both the prelude and the fugue are in 4/4 time. It was dedicated to his sister Nannerl, but the score given to her has not survived.

The prelude transitions from Adagio to Andante to Più Adagio, then returns to the initial tempo. The prelude begins with the tonic chord, featuring elaborate ornamentation and dynamic contrasts. In the Andante, the same chord is repeated in triplets, while the range and figuration are rich in variety. In the Più Adagio section, arpeggios of diminished seventh chords stand out.

The fugue is Andante maestoso, and Mozart instructed his sister not to play it too quickly. The subject is presented in the order of bass → alto → soprano, and the counter-subject is characterized by sequences. After expansions and contractions of the subject, it concludes by changing to Adagio.