The hexatonic, or six-note, blues scale consists of the minor pentatonic scale plus the ♭5th degree. A major feature of the blues scale is the use of blue notes, however, since blue notes are considered alternative inflections, a blues scale may be considered to not fit the traditional definition of a scale. At its most basic, a single version of this "blues scale" is commonly used over all changes (or chords) in a twelve bar blues progression. Likewise, in contemporary jazz theory, its use is commonly based upon the key rather than the individual chord. The evolution of this scale may be traced back to Asia (pentatonic major) through native North America (pentatonic minor) with the addition of the flat 5 blue note (slave trade/Africa).
Greenblatt defines two blues scales, the major and the minor. The major blues scale is C, D, D♯/E♭, E, G, A and the minor is C, D♯/E♭, F, F♯/G♭, G, B♭. The latter is the hexatonic scale (top).
The heptatonic, or seven-note, conception of the "blues scale" is as a diatonic scale (a major scale) with lowered third, fifth, and seventh degrees and blues practice is derived from the "conjunction of 'African scales' and the diatonic western scales". Steven Smith argues that, "to assign blue notes to a 'blues scale' is a momentous mistake, then, after all, unless we alter the meaning of 'scale'". It is the 2nd mode of the Harmonic Major scale.
An essentially nine note blues scale is defined by Benward and Saker as a chromatic variation of the major scale featuring a flat third and seventh degrees which, "alternating with the normal third and seventh scale degrees are used to create the blues inflection. These 'blue notes' represent the influence of African scales on this music."[better source needed]
A different and "non-formal" way of playing the scale is possible by use of "quarter step", added to 3rd and 7th degree of minor blues scale. For example, the scale "Blues A minor" will be as: A B C(+1/4) D E F# G(+1/4 ). Also, the notes D# can be used as an additional note. Guitar players can add a quarter step to a given note by bend technique.
In jazz, the blues scale is used by improvising musicians in a variety of harmonic contexts. It can be played for the entire duration of a twelve bar blues progression constructed off the root of the first dominant seventh chord. For example, a C hexatonic blues scale could be used to improvise a solo over a C blues chord progression. The blues scale can also be used to improvise over a minor chord. Jazz educator Jamey Aebersold describes the sound and feel of the blues scale as ‘funky,’ ‘down-home,’ ‘earthy,’ or ‘bluesy.’ 
The blues scale is also used in other genres to reference the blues idiom.
- Ferguson, Jim (2000). All Blues Scale for Jazz Guitar: Solos, Grooves & Patterns, p.6. ISBN 0-7866-5213-6.
- Arnold, Bruce (2002). The Essentials: Chord Charts, Scales and Lead Patterns for Guitar, p.8. ISBN 1-890944-94-7.
- Harrison, Mark (2003). Blues Piano: Hal Leonard Keyboard Style Series, p.8. ISBN 0-634-06169-0.
- "The Pentatonic and Blues Scale". How To Play Blues Guitar. 2008-07-09. Retrieved 2008-07-11.
- J. Bradford Robinson/Barry Kernfeld. "Blue Note", The New Grove Dictionary of Jazz, Second Edition, London (2002)
- "Blues Licks From Blues Scales". Between the Licks. 2008-02-25. Retrieved 2008-06-24.
- Greenblatt, Dan (2011). The Blues Scales - Eb Version, p.?. ISBN 9781457101472.
- Smallwood, Richard (1980). "Gospel and Blues Improvisation" p.102, Music Educators Journal, Vol. 66, No. 5. (Jan., 1980), p.100-104.
- Oliver, Paul. "That Certain Feeling: Blues and Jazz... in 1890?" p.13, Popular Music, Vol. 10, No. 1, The 1890s. (Jan., 1991), pp. 11-19. Cites Rudi Blesh.
- Smith, Steven G. (1992). "Blues and Our Mind-Body Problem", Popular Music, Vol. 11, No. 1. (Jan., 1992), pp. 41-52.
- Benward & Saker (2003). Music: In Theory and Practice, Vol. I, p.39. Seventh Edition. ISBN 978-0-07-294262-0.
- Aebersold, J. ‘How to Play Jazz and Improvise: Volume One’ (1967)
- Hewitt, Michael. 2013. Musical Scales of the World,[page needed]. The Note Tree. ISBN 978-0957547001.
- Blues Scale diagrams for guitar mapped out in all positions
- Blues Guitar Lessons - Pentatonic & Blues Scale
- The Jazz Resource How to play on the blues scale
- Slowhand Blues guitar Detailed information on Blues scales
- Blues Scales on Guitar Lesson with blues backing tracks
- Blues Guitar Discussing the theory of the blues and pentatonic scale