B-flat major is a major scale based on B♭, with pitches B♭, C, D, E♭, F, G, and A. Its key signature has two flats. Its relative minor is G minor and its parallel minor is B-flat minor.

The B-flat major scale is:

Many transposing instruments are pitched in B-flat major, including the clarinet, trumpet, tenor saxophone, and soprano saxophone. As a result, B-flat major is one of the most popular keys for concert band compositions.

• Tonic - B-flat major
• Supertonic - C minor
• Mediant - D minor
• Subdominant - E-flat major
• Dominant - F major
• Submediant - G minor
• Leading-tone - A diminished

Joseph Haydn's Symphony No. 98 is often credited as the first symphony written in that key, including trumpet and timpani parts. However, his brother Michael Haydn wrote one such symphony earlier, No. 36. Nonetheless, Joseph Haydn still gets credit for writing the timpani part at actual pitch with an F major key signature (instead of transposing with a C major key signature), a procedure that made sense since he limited that instrument to the tonic and dominant pitches.^[1] Many editions of the work use no key signature and specify the instrument as "Timpani in B♭–F".