An octotonic scale is any scale which contains eight individual pitches per octave rather than the seven found in common scales and modes.
The most commonly found octotonic scale is a scale comprised of alternating tones and semitones. It is a mode of limited transposition, having only three possible pitch-class sets, and also contains the pitches of two different diminished seventh chords. For this reason it is sometimes known as the diminished scale.
<music> c8 (cis dis e fis g a bes) </music> An octotonic scale with alternating tones and semitones, starting on C
The use of this octotonic scale became popular with Russian nationalist composers in the late nineteenth century, as a way of creating mystical and exotic-sounding melodies. It was also widely used by Igor Stravinsky in works such as Petrushka, The Rite of Spring and Symphonies of Wind Instruments. The use of octotonic scales is also present in works by Bela Bartok and Alexander Scriabin.