B-flat minor
Minor key with five flats; relative major is D-flat major.
What it means
B-flat minor is the minor key with five flats in its key signature: B♭, E♭, A♭, D♭, and G♭. Its tonic is B♭, and its relative major is D-flat major, which shares the same key signature.
On the circle of fifths, B-flat minor sits five steps on the flat side, next to E-flat minor and F minor.
Musical use
Since the 18th and 19th centuries, many key-character theories described B-flat minor as somber and mournful; Christian Friedrich Daniel Schubart, in his catalog of key characteristics, associated it with despair and thoughts of night. Such characterizations reflect the listening habits of their time rather than an objective property of the key, but they shaped composers' choices for serious, lamenting movements.
In piano literature, B-flat minor is best known through Frédéric Chopin's Piano Sonata No. 2, with its famous funeral march. It should be distinguished from the parallel major key of B-flat major, which shares only the tonic, and from its relative major, D-flat major, which shares the key signature but has a different tonal center.
Performance practice
Practice the harmonic and melodic minor forms of B-flat minor separately, since the sixth and seventh degrees differ depending on direction. At the piano, note the many black keys in the natural minor scale; on a string instrument, it helps to first find the relative major, D-flat major, and build the minor scale on B♭ from there.