In jazz and blues, a blue note (also "worried" note) is a note sung or played at a slightly lower pitch than that of the major scale for expressive purposes. Typically the alteration is a semitone or less, but this varies among performers and genres. Country blues, in particular, features wide variations from the diatonic pitches with emotive blue-notes. Blue notes are often seen as akin to relative pitches found in traditional African work songs.

The blue notes are usually said to be the flattened third, flattened fifth, and flattened seventh scale degrees. Though the blues scale has "an inherent minor tonality, it is commonly 'forced' over major-key chord changes, resulting in a distinctively dissonant conflict of tonalities". A similar conflict occurs between the notes of the minor scale and the minor blues scale, as heard in songs such as "Why Don't You Do Right?."

In the case of the flattened third over the root (or the flattened seventh over the dominant), the resulting chord is a neutral mixed third chord.