Nocturne Op. 9 No. 1, in Bb Minor

One of the better known nocturnes, this piece has a rhythmic freedom that came to characterize Chopin's later work. The left hand has an unbroken sequence of eighth notes in simple arpeggios throughout the entire piece, while the right hand moves with freedom, occasionally in patterns of seven, eleven, twenty, and twenty-two in the form of polyrhythms. The piece is 85 measures long and in 6/4 meter. It is written in ternary form; after the primary theme, the secondary theme starts in measure 19, followed by a modified version of the primary theme in measure 70.

The opening section moves into a contrasting middle section in the same key signature, which flows back to the opening material in a transitional passage where the melody floats above seventeen consecutive bars of Db major chords. The reprise of the first section grows out of this, followed by a Picardy third ending.