Preludes are a series of short pieces including all 24 keys. Chopin created his preludes in the winter of 1838/39 in Majorca. Chopin usually played a couple of preludes at the beginning of his recitals in Paris and London. Today, they are played in groups or as a whole.
Besides the series of 24 Preludes there is one more separate Prelude.
24 Preludes Op. 28 in: C Major, a minor, G Major, e minor, D Major, b minor, A Major,
f sharp minor, E Major, c sharp minor, B Major, g sharp minor, F sharp Major, e flat minor, D flat Major, b flat minor, A flat Major, f minor, E flat Major, c minor, B flat Major, g minor, F Major, d minor
Prelude in c sharp minor Op. 45